Heme/coag/UA Flashcards

Question

Which of the following statistical terms reflects the best index of precision when comparing two complete blood count (CBC) parameters? A. Mean B. Median C. Coefficient of variation D. Standard deviation

Answer 1

C Standard deviation(s) describes the distribution of a sample of observations. It depends on the dispersion of results and is most influenced by reproducibility or precision. Because s is influenced by the mean, the coefficient of variation ([s ÷ mean] × 100) can be used to compare precision of tests with different means

Answer 2

D Deoxyhemoglobin is the physiological Hgb that results from the unloading of O2 by Hgb. This is accompanied by the widening of the space between β-chains and the binding of 2,3-diphosphoglycerate (2,3-DPG) on a mole-for-mole basis

Answer 3

A Acidosis is associated with a shift to the right of the oxyhemoglobin dissociation curve and, therefore, increased O2 release (decreased affinity of Hgb for O2). Alkalosis does the opposite. Multiple blood transfusions shift the curve to the left because transfused blood is low in 2,3-DPG. Hgb S and Hgb C do not change the affinity of O2 for Hgb; however, many hemoglobinopathies do. For example, Hgb Kansas causes a right shift, and Hgb Chesapeake causes a left shift of the oxyhemoglobin dissociation curve.

Answer 4

B In aplastic anemia, lymphocytes constitute the majority of the nucleated cells seen. In aplastic anemia, bone marrow is spotty, with patches of normal cellularity. Absolute granulocytopenia is usually present; however, lymphocyte production is less affected.

Answer 5

C The normal adult percentage of lymphocytes in a WBC differential is between 20% and 44%, although normal ranges vary by institution, patient population, and testing methodology. This range is higher in the pediatric population.

Answer 6

A There is relative neutropenia in children from ages 4 months to 4 years. Because of this, the percentage of lymphocytes is increased in this population. This is commonly referred to as a reversal in the normal differential percentage (or inverted differential)

Answer 7

C A relative monocyte count of 15% is abnormal, given that the baseline monocyte count in a normal differential is between 1% and 8%. An increased monocyte count may signal a myeloproliferative process, such as chronic myelomonocytic leukemia, an inflammatory response, or abnormal lymphocytes that may have been counted as monocytes by an automated cell counter

Answer 8

D In normal erythrocytic maturation, Hgb formation in the late polychromatic normoblast stage gives the cytoplasm a prominent pink coloration. The RBC continues to produce Hgb throughout the reticulocyte stage of development

Answer 9

C The structure of Hgb H is β4. Hgb H disease is a severe clinical expression of α- thalassemia in which only one α-gene out of four is functioning.

Answer 10

D Increases in 2,3-DPG, acidosis, and hypoxia and rise in body temperature all shift the Hgb O2 dissociation curve to the right. In anemia, although the number of RBCs is reduced, the cells are more efficient at O2 delivery because there is an increase in RBC 2,3-DPG. This causes the oxyhemoglobin dissociation curve to shift to the right, allowing more O2 to be released to tissues.

Answer 11

D Autoagglutination at room temperature may cause a low RBC count and high MCV from an electronic counter. The Hct will be low because it is calculated from the RBC count. Low RBC count and low Hct cause falsely high values of MCH and MCHC, respectively.

Answer 12

C Hypersplenic conditions are generally described by the following four criteria: (1) cytopenias of one or more peripheral cell lines, (2) splenomegaly, (3) bone marrow hyperplasia, and (4) resolution of cytopenia by splenectomy.

Answer 13

B The spleen is the supreme filter of the body, pitting imperfections from the erythrocyte without destroying the integrity of the membrane.

Answer 14

D Spherocytes lose their deformability because of a defect in spectrin, a membrane protein, and are therefore prone to splenic sequestration and hemolysis

Answer 15

C Classic features of intravascular hemolysis, such as hemoglobinemia, hemoglobinuria, or hemosiderinuria, do not occur in HS. The hemolysis seen in HS is an extravascular process, rather than an intravascular process.

Answer 16

D Spherocytic cells have decreased tolerance to swelling and, therefore, hemolyse at a higher concentration of sodium salt compared with normal RBCs.

Answer 17

C. Sickle cell disease is a chronic hemolytic anemia classified as a normocytic, normochromic anemia.

Answer 18

D The major Hgb in sickle cell trait is Hgb A, which constitutes 50% to 70% of the total. Hgb S comprises 20% to 40%, and Hgb A2 and Hgb F are present in normal amounts.

Answer 19

B The structural mutation for Hgb S is the substitution of valine for glutamic acid at the sixth position of the β-chain. Because glutamic acid is negatively charged, this decreases its rate of migration toward the anode at pH 8.6.

Answer 20

D Substitution of a positively charged amino acid for a negatively charged amino acid in Hgb C disease results in a slower electrophoretic mobility at pH 8.6.

Answer 21

C At pH 8.6, several Hgbs migrate together. These include Hgb A2, Hgb C, Hgb E, Hgb 0Arab, and Hgb CHarlem. These are located nearest the cathode at pH 8.6

Answer 22

B Electrophoresis at alkaline pH usually shows 50% to 70% Hgb A, 20% to 40% Hgb S, and normal levels of Hgb A2 in a patient with the sickle cell trait.

Answer 23

D Autosplenectomy occurs in sickle cell anemia as a result of repeated infarcts to the spleen caused by an overwhelming sickling phenomenon

Answer 24

A PNH is a rare acquired stem cell disorder that results in abnormalities of the RBC membrane. This causes the RBCs to become highly sensitive to complement-mediated hemolysis. Because this is a stem cell disorder, abnormalities are seen in leukocytes and PLTs, as well as in RBCs. PNH is characterized by recurrent, episodic intravascular hemolysis, hemoglobinuria, and venous thrombosis.

Answer 25

D Hemolytic anemia of HUS is associated with reticulocytosis. The anemia seen in HUS is multifactorial, with characteristic thrombocytopenia, schistocytes, and polychromasia commensurate with the anemia.

Answer 26

D The autohemolysis test result is positive in G6PD and PK deficiencies and in HS but is normal in PNH because lysis in PNH requires sucrose to enhance complement binding. The addition of glucose, sucrose, or adenosine triphosphate (ATP) corrects autohemolysis of HS. Autohemolysis of PK can be corrected by ATP.

Answer 27

D PCH is caused by the anti-P antibody, a cold autoantibody that binds to the patient’s RBCs at low temperatures and fixes complement. In the classic Donath–Landsteiner test, hemolysis is demonstrated in a sample placed at 4°C then warmed to 37°C.

Answer 28

A Methemoglobin occurs when iron is oxidized to the ferric state. Normally, iron is predominantly in the ferrous state in the Hgb that circulates. During intravascular hemolysis, the RBCs rupture, releasing Hgb directly into the bloodstream. Haptoglobin is a protein that binds to free Hgb. The increased free Hgb in intravascular hemolysis causes depletion of haptoglobin. As haptoglobin is depleted, unbound Hgb dimers appear in the plasma (hemoglobinemia) and are filtered through the kidneys and reabsorbed by the renal tubular cells. The renal tubular uptake capacity is approximately 5 g/day of filtered Hgb. Beyond this level, free Hgb appears in urine (hemoglobinuria). Hemoglobinuria is associated with hemoglobinemia

Answer 29

B Spherocytes are characteristic of AIHA and cause increased osmotic fragility. In AIHAs, production of autoantibodies against one’s own RBCs causes hemolysis or phagocytic destruction of RBCs. A positive direct antiglobulin (DAT or Coombs’) test identifies in vivo antibody-coated and complement-coated RBCs. A positive DAT result distinguishes AIHA from other types of hemolytic anemia that produce spherocytes.

Answer 30

C In patients with G6PD deficiency, the RBCs are unable to reduce nicotinamide adenine dinucleotide phosphate (NADP); consequently, Hgb is denatured, and Heinz bodies are formed. “Bite cells” appear in the peripheral circulation as a result of splenic pitting of Heinz bodies.

Answer 31

C RBC indices classify the anemia morphologically. Anemias can be classified morphologically by using laboratory data; physiologically, based on the mechanism; and clinically, based on an assessment of symptoms

Answer 32

C Aplastic anemia has many causes, such as chemical, drug, or radiation poisoning; congenital aplasia; and Fanconi syndrome. All result in depletion of hematopoietic precursors of all cell lines, leading to peripheral blood pancytopenia.

Answer 33

A There are four classifications of CDAs, each characterized by ineffective erythropoiesis, increased unconjugated bilirubin, and bizarre multinucleated erythroid precursors.

Answer 34

D Microangiopathic hemolytic anemia is a condition resulting from shear stress to the erythrocytes. Fibrin strands are laid down within the microcirculation, and RBCs become fragmented as they contact fibrin through the circulation process, forming schistocytes.

Answer 35

D Chloramphenicol is the drug most often implicated in acquired aplastic anemia. About half the cases occur within 30 days after therapy, and about half are reversible. Penicillin, tetracycline, and sulfonamides have been implicated in a small number of cases.

Answer 36

A Sickle cell disorders are intracorpuscular RBC defects that are hereditary and result in defective Hgbs being produced. The gene for sickle cell can be inherited either homozygously or heterozygously.

Answer 37

C Spherocytes are produced in AIHA. Spherocytes may be produced by one of three mechanisms. First, they are a natural morphological phase of normal RBC senescence. Second, they are produced when the cell surface:volume ratio is decreased, as seen in HS. And, third, they may be produced as a result of antibody coating of RBCs. As the antibody-coated RBCs travel through the spleen, the antibodies and portions of the RBC membrane are removed by macrophages. The membrane repairs itself; hence, the RBC’s morphology changes from a biconcave disk to a spherocyte.

Answer 38

C This patient’s abnormal peripheral blood smear indicates marked RBC regeneration, causing many reticulocytes to be released from bone marrow. Because reticulocytes are larger than mature RBCs, MCV will be slightly elevated.

Answer 39

B As a result of splenectomy, Howell–Jolly bodies may be seen in great numbers. One of the main functions of the spleen is pitting, which allows inclusions to be removed from the RBC without destroying the cell membrane.

Answer 40

D Reticulocytes are polychromatophilic macrocytes, and the presence of reticulocytes indicates RBC regeneration. Bone marrow’s appropriate response to anemia is to deliver RBCs prematurely to the peripheral circulation. In this way, reticulocytes and possibly NRBCs may be seen in the peripheral blood smear.

Answer 41

C HP is a membrane defect characterized by a spectrin abnormality and thermal instability. MCV is decreased, and RBCs appear to be budding and fragmented.

Answer 42

B Osmotic fragility is decreased because numerous target cells are present and have increased surface volume in patients with thalassemia major.

Answer 43

C In IDA, there is an increase in TIBC and in RBC protoporphyrin. Serum iron and ferritin levels are decreased. IDA is characterized by a microcytic hypochromic anemia.

Answer 44

D In IDA, serum iron and ferritin levels are decreased, and TIBC and RBC protoporphyrin are increased. In chronic disease, serum iron and TIBC are both decreased because the iron is trapped in reticuloendothelial (RE) cells and is unavailable to RBCs for Hgb production.

Answer 45

B Thalassemia and IDA are both classified as microcytic, hypochromic anemias. IDA is caused by defective heme synthesis, whereas thalassemia is caused by decreased globin chain synthesis.

Answer 46

A IDA is characterized by decreased plasma iron, increased TIBC, decreased % saturation, and microcytic, hypochromic anemia. Iron deficiency occurs in three phases: iron depletion, iron-deficient erythropoiesis, and IDA

Answer 47

D Ferritin enters serum from all ferritin-producing tissues and, therefore, is considered a good indicator of body storage iron. Because iron stores must be depleted before anemia develops, low serum ferritin levels precede the fall in serum iron associated with IDA.

Answer 48

D Sideroblastic anemias are a group of disorders characterized by hypochromic anemia, ineffective erythropoiesis, an increase in serum and tissue iron, and the presence of ringed sideroblasts in bone marrow

Answer 49

C In thalassemia major, there is little or no production of the β-chain, resulting in severely depressed or no synthesis of Hgb A. Severe anemia is seen, along with skeletal abnormalities and marked splenomegaly. The patient is usually supported with transfusion therapy.

Answer 50

D Patients with thalassemia major are unable to synthesize the β-chain; hence, little or no Hgb A is produced. However, γ-chains continue to be synthesized and lead to variable elevations of Hgb F in these patients.

Answer 51

C The indices will provide a morphological classification of this anemia. MCV is 75 fL (reference range 80–100 fL), MCH is 20 pg (reference range 27–31 pg), and MCHC is 26.6% (reference range 32%–36%). Therefore, the anemia is microcytic hypochromic.

Answer 52

C Hgb A2 is part of the normal complement of adult Hgb. This Hgb is elevated in β- thalassemia minor because the individual with this condition has only one normal β- gene; consequently, there is a slight elevation of Hgb A2 and Hgb F.

Answer 53

B Thirty to fifty percent of the individuals with anemia of chronic inflammation demonstrate a microcytic hypochromic blood picture, with decrease in serum iron. Serum iron is decreased because it is unable to escape from the RE cells to be delivered to the NRBCs in bone marrow.

Answer 54

D Megaloblastic anemia is macrocytic normochromic because there is no defect in Hgb synthesis. These anemias comprise a group of asynchronized anemias characterized by defective nuclear maturation resulting from defective DNA synthesis. This abnormality accounts for the megaloblastic features in bone marrow and macrocytosis in peripheral blood

Answer 55

D Pernicious anemia is caused by lack of intrinsic factor, which prevents vitamin B12 absorption

Answer 56

B Megaloblastic anemias are associated with ineffective erythropoiesis and, therefore, a decrease in the reticulocyte count

Answer 57

B Administration of folic acid to a patient with vitamin B12 deficiency will correct the hematological abnormalities, but the neurological problems will persist. This helps confirm the correct diagnosis of vitamin B12 deficiency.

Answer 58

D Ineffective erythropoiesis is caused by destruction of erythroid precursor cells prior to their release from bone marrow. Pernicious anemia results from defective DNA synthesis; it is suggested that the asynchronous development of RBCs renders them more prone to intramedullary destruction.

Answer 59

D Patients with pernicious anemia demonstrate pancytopenia with low WBC, PLT, and RBC counts. Because this is a megaloblastic process and a DNA maturation defect, all cell lines are affected. In bone marrow, this results in abnormally large precursor cells, maturation asynchrony, hyperplasia of all cell lines, and a low M:E ratio.

Answer 60

B Patients with obstructive liver disease may have macrocytes on their peripheral blood smear because of an increased tendency toward deposition of lipid on the surface of RBCs. Consequently, the RBCs are larger or more macrocytic than normal RBCs.

Answer 61

C Macrocytes in true megaloblastic conditions are oval, as opposed to the round shape of macrocytes usually seen in alcoholism and obstructive liver disease.

Answer 62

C The RBC indices in a patient with megaloblastic anemia are macrocytic and normochromic. The macrocytosis is prominent, with MCV ranging from 100 to 130 fL.

Answer 63

B The patient will have increased MCV. One of the causes of a macrocytic anemia that is not megaloblastic is increased reticulocyte count, here noted as increased polychromasia. Reticulocytes are polychromatic macrocytes; therefore, MCV is slightly increased.

Answer 64

C Occasionally patients with infectious mononucleosis develop a potent cold agglutinin with anti-I specificity. This cold autoantibody can cause strong hemolysis and hemolytic anemia

Answer 65

C HIV infection brings about several hematological abnormalities seen on peripheral blood smear examination; most patients demonstrate reactive lymphocytes and have granulocytopenia.

Answer 66

A Döhle bodies are RNA-rich areas within polymorphonuclear neutrophils (PMNs) that are oval and light blue. Although often associated with infectious states, they are seen in a wide range of conditions and toxic reactions, including hemolytic and pernicious anemias, chronic granulocytic leukemia, and therapy with antineoplastic drugs. The other inclusions are associated with erythrocytes.

Answer 67

B Myeloperoxidase, lysozyme, and acid phosphatase are enzymes that are contained in the primary granules of neutrophils. The contents of secondary and tertiary granules include lactoferrin, collagenase, NADPH oxidase, and alkaline phosphatase.

Answer 68

D The mean relative lymphocyte percentage for a 1-year-old child is 61% compared with the mean lymphocyte percentage of 35% in an adult.

Answer 69

B Neutrophil changes associated with infection may include neutrophilia, shift to the left, toxic granulation, Döhle bodies, and vacuolization. Pelgeroid hyposegmentation is noted in neutrophils from individuals with congenital Pelger–Huët anomaly and those with an acquired anomaly induced by drug ingestion or secondary to certain conditions, such as leukemia.

Answer 70

A Neutropenia is defined as an absolute decrease in the number of circulating neutrophils. This condition is present in patients having neutrophil counts of less than 1.5 × 10^9/L.

Answer 71

B Chédiak–Higashi syndrome is a disorder of neutrophil phagocytic dysfunction caused by depressed chemotaxis and delayed degranulation. The degranulation disturbance is attributed to interference from the giant lysosomal granules characteristic of this disorder.

Answer 72

C Pelger–Huët anomaly is a benign familial condition reported in 1 out of 6,000 individuals. Care must be taken to differentiate Pelger–Huët cells from the numerous band neutrophils and metamyelocytes that may be observed during severe infection or a shift-to-the-left of immaturity in granulocyte stages

Answer 73

D If both the heterophile antibody test and the EBV-IgM tests yield negative results in a patient with reactive lymphocytosis and a suspected viral infection, serum should be analyzed for IgM antibodies to CMV. CMV belongs to the herpes virus family and is endemic worldwide. CMV infection is the most common cause of heterophile-negative infectious mononucleosis

Answer 74

A The biochemical products of the respiratory burst involved in neutrophil particle ingestion during phagocytosis are H2O2 and O2–. The activated neutrophil discharges the enzyme NADPH oxidase into the phagolysosome, where it converts O2 to O2–, which is then reduced to H2O2.

Answer 75

D Both reactive lymphocytes and blasts may have basophilic cytoplasm, a high N:C ratio, and the presence of prominent nucleoli. Blasts, however, have an extremely fine nuclear chromatin staining pattern as viewed on a Wright– and Giemsa–stained smear.

Answer 76

B Auer rods are not seen characteristically in lymphoblasts. They may be seen in myeloblasts, promyelocytes, and monoblasts

Answer 77

C Acute leukemia is usually associated with a normocytic normochromic anemia. Anemia in acute leukemia is usually present from the onset and may be severe; however, there is no inherent nutritional deficiency leading to a microcytic, hypochromic, or megaloblastic process.

Answer 78

C The presence of immature leukocytes and NRBCs is called leukoerythroblastosis and frequently denotes a malignant or myeloproliferative process. Myelophthisis refers to replacement of bone marrow by a disease process, such as a neoplasm. The development of abnormal tissue is called dysplasia.

Answer 79

D A normal physiological response to anemia would be an increase in the kidney’s production of erythropoietin. The accumulation of leukemic cells in bone marrow leads to marrow failure, which manifests as anemia, thrombocytopenia, and granulocytopenia.

Answer 80

D Acute monocytic leukemia has an incidence of 1% to 8% of all acute leukemias. It has a distinctive clinical manifestation of monocytic involvement, resulting in skin and gum hyperplasia. The WBC count is markedly elevated, and prognosis is poor

Answer 81

A ALL usually affects children from ages 1 to 15 years and is the most common type of acute leukemia in this age group. In addition, ALL constitutes the single most prevalent malignancy in pediatric patients.

Answer 82

B In patients with acute PML, the azurophilic granules in the leukemic promyelocytes contain thromboplastic substances. When released from promyelocytes, these activate soluble coagulation factors causing DIC

Answer 83

B A disproportionate increase in the myeloid component of bone marrow is usually the result of a leukemic state. The normal M:E ratio is approximately 4:1 in adults with normal cellularity.

Answer 84

A Auer rods are a linear projection of primary azurophilic granules and are present in the cytoplasm of myeloblasts and monoblasts in patients with acute leukemia.

Answer 85

C In acute erythroid leukemia, greater than 50% of nucleated bone marrow cells are erythroid and greater than 30% nonerythroid cells are blasts. Pernicious anemia results in pancytopenia and low vitamin B12 concentrations.

Answer 86

D Common signs of ALL are hepatosplenomegaly (65%), lymphadenopathy (50%), and fever (60%). Anemia and thrombocytopenia are usually present, and the WBC count is variable. The numerous lymphoblasts are generally PAS positive.

Answer 87

A AML blasts stain positive for SBB and peroxidase. Usually, less than 10% blasts are found in peripheral blood smears from patients with CML, unless there has been a transition to blast crisis. The organelles in the cells of AUL are not mature enough to stain positive for SBB or peroxidase. Blasts in ALL are characteristically negative with these stains

Answer 88

C Phospholipids, neutral fats, and sterols are stained by SBB. The PAS reaction stains intracellular glycogen. Myeloperoxidase is an enzyme present in the primary granules of myeloid cells and, to a lesser degree, in monocytic cells. TdT is a DNA polymerase found in thymus-derived lymphocytes and some bone marrow–derived lymphocytes.

Answer 89

B NASDA stains monocytes (and monoblasts) and granulocytes (and myeloblasts). The addition of fluoride renders monocytic cells (and blasts) negative, thus allowing for differentiation from granulocytic cells, which remain positive.

Answer 90

D The majority of non-T, non-B ALL blast cells display the CALLA marker. Lymphoblasts of common ALL are TdT positive and CALLA positive but do not have surface membrane IgM or μ-chains and are pre-B lymphoblasts. Common ALL has a lower relapse rate and better prognosis compared with other immunologic subtypes of B-cell ALL.

Answer 91

A PAS is positive in about 50% of ALL with L1 and L2 morphology but is negative in ALL with L3 morphology (B-cell ALL). TdT is positive in all types of ALL except L3. Both TdT and PAS are negative in AML

Answer 92

D SBB stains phospholipids and other neutral fats. It is the most sensitive stain for granulocytic precursors. Lymphoid cells rarely stain positive with SBB. Because 70% lymphoblasts would never be seen in CLL, the correct response is ALL.

Answer 93

D The WHO classification system includes the following disorders under MPN: CML, CNL, CEL, essential thrombocythemia (ET), PV, primary (idiopathic) myelofibrosis, hypereosinophilic syndrome, mast cell disease, and MPNs unclassified

Answer 94

B In addition to morphology, cytochemical stains, and flow cytometry, the WHO classification relies heavily on chromosomal and molecular abnormalities.

Answer 95

B The WHO classification of AML requires that 20% or greater of nucleated bone marrow cells be blasts, whereas the French–American-British (FAB) classification generally requires 30% or greater. The WHO classifies AML into five subgroups: acute myeloid leukemias with recurrent genetic disorders; acute myeloid leukemia with multilineage dysplasia; acute myeloid leukemia and myelodysplastic syndromes, therapy related; acute myeloid leukemia (not otherwise categorized); and acute leukemia of ambiguous lineage.

Answer 96

C AML with t(8;21) is classified under the category “AML with Recurrent Genetic Abnormalities” by the WHO. This translocation occurs in up to 15% of cases of AML and may be the most common translocation. The AML1–ETO translocation occurs chiefly in younger patients and often in cases of acute myeloblastic leukemia with maturation, FAB M2. The translocation involves the fusion of the AML1 gene on chromosome 21 with the ETO gene on chromosome 8.

Answer 97

A AML with t(15;17) is classified under the category “AML with Recurrent Genetic Abnormalities” by the WHO. Acute PML (known as M3 under the FAB system) is composed of abnormal promyelocytes with heavy granulation, sometimes obscuring the nucleus, and abundant cytoplasm. Acute PML contains a translocation that results in the fusion of a transcription factor called PML on chromosome 15 with the alpha (α)-retinoic acid receptor gene (RARα) on chromosome 17.

Answer 98

D AML with inv(16) has pericentric inversion of chromosome 16 and is associated with M4 with marrow eosinophilia, M4eo under the FAB system. The inv(16) results in the fusion of the CBFβ gene on 16q22 with the MYH11 gene on 16p13.

Answer 99

C Acute megakaryoblastic leukemia, which is equivalent to FAB M7, is a relatively uncommon form of leukemia characterized by neoplastic proliferation of megakaryoblasts and atypical megakaryocytes. Recognition of this entity was aided by the use of platelet peroxidase (PPO) ultrastructural studies. PPO is distinct from myeloperoxidase and is specific for the megakaryocytic cell line. Acute megakaryoblastic leukemia is defined as an acute leukemia in which 50% or greater of the blasts are of megakaryocytic lineage. In the WHO 2016 revision, it is classified under “AML (not otherwise categorized).”

Answer 100

C The most common treatment modality utilized in PV is phlebotomy. Reduction of blood volume (usually 1 unit of whole blood—450 cc) can be performed weekly or even twice weekly in younger patients to control symptoms. The Hct target range is less than 45% for men and less than 42% for women. IDA is a predictable complication of therapeutic phlebotomy because approximately 250 mg of iron is removed with each unit of blood.

Answer 101

A In ET, the PLT count is extremely elevated. These PLTs are abnormal in function, leading to both bleeding and thrombotic diathesis

Answer 102

D The morphological common denominator in Hodgkin lymphoma is the RS cell. It is a large, binucleated cell with a dense nucleolus surrounded by clear space. These characteristics give the RS cell an “owl’s eye” appearance. Niemann–Pick cells (foam cells) are histiocytes containing phagocytized sphingolipids that stain pale blue and impart a foamlike texture to the cytoplasm. Flame cells are plasma cells with a distinctive red cytoplasm. They are sometimes seen in the bone marrow of patients with multiple myeloma.

Answer 103

C The marked amount of fibrosis, both medullary and extramedullary, accounts for the irreversible change in RBC morphology to a teardrop shape. The RBCs are “teared” as they attempt to pass through the fibrotic tissue.

Answer 104

D The diagnosis of PV requires the demonstration of an increase in RBC mass. Pancytosis may also be seen in about two thirds of PV cases. Plasma volume is normal or slightly reduced, and arterial O2 saturation is usually normal.

Answer 105

A Splenomegaly is a feature of PV but not characteristic of secondary polycythemia. The RBC mass is increased in both primary polycythemia (PV) and secondary polycythemia. Erythropoietin is increased, and O2 saturation is decreased in secondary polycythemia.

Answer 106

B Relative polycythemia is caused by reduction of plasma, rather than an increase in RBC volume or mass. RBC mass is increased in both PV and secondary polycythemia, but erythropoietin levels are high only in secondary polycythemia

Answer 107

B PV is a myeloproliferative disorder characterized by uncontrolled proliferation of erythroid precursors. However, production of all cell lines is usually increased. Panhyperplasia is a term used to describe the cellularity of bone marrow in PV.

Answer 108

C One hundred mature neutrophils are counted and scored. The LAP score is calculated as follows: (the number of 1+ cells × 1) + (2+ cells × 2) + (3+ cells × 3) + (4+ cells × 4). That is, 48 + 76 + 9 + 4 = 137. The reference range is approximately 20 to 130.

Answer 109

A CML causes a low LAP score, whereas an elevated or normal score occurs in a leukemoid reaction. CML cannot be distinguished by WBC count because both CML and leukemoid reaction have a high count.

Answer 110

D Anemia, fibrosis, myeloid metaplasia, thrombocytosis, and leukoerythroblastosis occur in IMF.

Answer 111

B Ninety percent of patients with CML have the Ph1 chromosome. This appears as a long-arm deletion of chromosome 22 but is actually a translocation between the long arms of chromosomes 22 and 9. The ABL oncogene from chromosome 9 forms a hybrid gene with the bcr region of chromosome 22. This results in production of a chimeric protein with tyrosine kinase activity that activates the cell cycle. The prognosis for CML is better if the Ph1 chromosome is present. Often, a second chromosomal abnormality occurs in CML before a blast crisis.

Answer 112

D CML is marked by an elevated WBC count demonstrating various stages of maturation, hypermetabolism, and minimal LAP staining. An increase in basophils and eosinophils is a common finding. Pseudo–Pelger–Huët cells and thrombocytosis may be present. Bone marrow is hypercellular, with a high M:E ratio (e.g., 10:1).

Answer 113

D CML shows the least LAP activity, whereas the LAP score is slightly to markedly increased in each of the other states.

Answer 114

C The WBC count in CML is often higher than 100 × 109/L, and the peripheral blood smear shows granulocyte progression from myeloblast to segmented neutrophil.

Answer 115

D Splenomegaly is seen in greater than 90% of patients with CML, but it is not a characteristic finding in AML. Infections, hemorrhage, and elevated WBC counts may be seen in both CML and AML.

Answer 116

D Osteolytic lesions indicating destruction of bone, as evidenced by radiography, are seen in multiple myeloma but not in Waldenström macroglobulinemia. In addition, Waldenström macroglobulinemia gives rise to lymphocytosis, which does not occur in multiple myeloma, and differs in the morphology of the malignant cells

Answer 117

C Rouleaux is present in patients with multiple myeloma as a result of increased viscosity and decreased albumin:globulin ratio. Multiple myeloma is a plasma cell dyscrasia that is characterized by overproduction of monoclonal immunoglobulin.

Answer 118

D The Ph1 chromosome is a diagnostic marker for CML. Osteolytic lesions, monoclonal gammopathy, and bone marrow infiltration by plasma cells constitute the triad of diagnostic markers for multiple myeloma.

Answer 119

C Benign monoclonal gammopathies have peripheral blood findings similar to those in myeloma. However, a lower concentration of monoclonal protein is usually seen. There are no osteolytic lesions, and the plasma cells comprise less than 10% of nucleated cells in bone marrow. About 30% become malignant, and therefore the term monoclonal gammopathy of undetermined significance (MGUS) is the designation used to describe this condition

Answer 120

D Mutated plasmablasts in bone marrow undergo clonal replication and expand the plasma cell mass. Normal bone marrow is gradually replaced by malignant plasma cells, leading to pancytopenia. Most malignant plasma cells actively produce immunoglobulins. In multiple myeloma, the normally controlled and purposeful production of antibodies is replaced by inappropriate production of even larger amounts of useless immunoglobulin molecules. The normally equal production of light chains and heavy chains may be imbalanced. The result is the release of excess free light chains or free heavy chains. The immunoglobulins produced by a single clone of myeloma cells are identical. Any abnormal production of identical antibodies is referred to by the general term monoclonal gammopathy. Osteoclasts are bone cells active in locally resorbing bone and releasing calcium into blood. Nearby osteoblasts are equally active in utilizing the calcium in blood to form new bone. Multiple myeloma interrupts this balance by the secretion of at least two substances. These are interleukin-6 (IL-6) and OAF. As its name implies, OAF stimulates osteoclasts to increase bone resorption and release of calcium, which lead to lytic lesions of the bone.

Answer 121

A Waldenström macroglobulinemia is a malignancy of lymphoplasmacytoid cells, which manufacture IgM. Although the cells secrete immunoglobulin, they are not fully differentiated into plasma cells and lack the characteristic perinuclear halo, deep basophilia, and eccentric nucleus characteristic of classic plasma cells

Answer 122

C A variable number of malignant cells in HCL will stain positive with tartrate-resistant acid phosphatase (TRAP+). Although this cytochemical reaction is fairly specific for HCL, TRAP activity has occasionally been reported in B-cell leukemia and, rarely, T- cell leukemia.

Answer 123

D The JAK2(V617F) mutation is negative in patients with CML. It may be positive in patients with IMF (35%–57%), PV (65%–97%), and ET (23%–57%).

Answer 124

D In the revised 2016 WHO classification, diagnosis of ET requires meeting four major WHO diagnostic criteria, which include: PLT count 450 × 109/L or greater; bone marrow proliferation of megakaryocyte lineage with large and mature megakaryocytes with hyperlobulated nuclei and no or little granulocyte or erythroid proliferation; not meeting WHO criteria for CML, PV, PMF, MDS, or other myeloid neoplasm; and demonstration of JAK2(V617F), CALR, or MPL mutation or other clonal marker. Diagnosis can also be made with the first three major criteria and one minor criterion, either evidence of clonality or absence of reactive thrombocytosis

Answer 125

B The formula for correcting the WBC count for the presence of NRBCs is: Total WBC × 100 or (21.0 × 100) ÷ 126 = 16.7 × 10^9/L where total WBC = WBCs × 10^9/L, 100 is the number of WBCs counted in the differential, and 126 is the sum of NRBCs plus WBCs counted in the differential.

Answer 126

# cells counted × 10 (depth factor) × dilution factor ÷ area counted in mm2 or C The formula for calculating manual cell counts using a hemacytometer is: # cells counted × 10 (depth factor) × dilution factor ÷ area counted in mm2 or (80 × 10 × 100) ÷ 4 = 20,000/μL or 20.0 × 10^9/L

Answer 127

D Regardless of the cell or fluid type, the formula for calculating manual cell counts using a hemacytometer is: # cells counted × 10 (depth factor) × dilution factor ÷ area counted in mm2 or (125 × 10 × 200) ÷ 1 = 250,000/μL or 250.0 × 10^9/L

Answer 128

A WBC identification is facilitated by analysis of the impedance, conductance, and light- scattering properties of WBCs. The scatterplot represents the relationship between volume (x-axis) and light scatter (y-axis). Monocytes account for the dots in section A, neutrophils are represented in section B, eosinophils are represented in section C, and lymphocytes are denoted in section D.

Answer 129

C When an automated WBC count is performed using a hematology analyzer, RBCs are lysed to allow enumeration of WBCs. Sickle cells are often resistant to lysis within the limited time frame (less than 1 minute), during which the RBCs are exposed to the lysing reagent and the WBCs are subsequently counted. As a result, the nonlysed RBCs are counted along with WBCs, and this falsely increases the WBC count. When an automated cell counting analyzer indicates a review flag for the WBC count and sickle cells are noted on peripheral blood smear analysis, a manual WBC count must be performed. The manual method allows optimal time for sickle cell lysis and accurate enumeration of WBCs.

Answer 130

D During the first week of life, an infant has an average Hct of 55 mL/dL. This value drops to a mean of 43 mL/dL by the first month of life. The mean MCV of the first week is 108 fL; after 2 months, the average MCV is 96 fL. The mean WBC count during the first week is approximately 18 × 10^9/L, and this drops to an average of 10.8 × 10^9/L after the first month. The PLT count in newborns falls within the same normal range as in adults.

Answer 131

A Lymphocytosis with numerous atypical lymphocytes is a hallmark finding consistent with the diagnosis of infectious mononucleosis. The automated results demonstrated abnormal WBC subpopulations, specifically lymphocytosis as well as monocytosis. However, on peripheral blood smear examination, 60 atypical lymphocytes and only six monocytes were noted. Atypical lymphocytes are often misclassified by automated cell counters as monocytes. Therefore, the automated analyzer differential must not be released and the manual differential count must be relied on for diagnostic interpretation.

Answer 132

B The “+++++” on the printout indicates that the WBC count exceeds the upper linearity of the analyzer (greater than 99.9 × 10^9/L). This markedly elevated WBC count, combined with the spectrum of immature granulocytic cells seen on peripheral blood smear examination, indicates the diagnosis of CML

Answer 133

D All of the automated results have “R,” or review, flags indicated; none can be released without manual verification procedures. The specimen must be diluted to bring the WBC count within the linearity range of the analyzer. When enumerating the RBC count, the analyzer does not lyse the WBCs and, in fact, includes them in the RBC count. As such, the RBC count is falsely elevated because of the increased number of WBCs. Therefore, after an accurate WBC count has been obtained, this value can be subtracted from the RBC count to obtain the true RBC count. For example, using the values for this patient: Step 1: Obtain an accurate WBC count by diluting the sample 1:10. WBC = 41.0 × 10 (dilution) = 410 × 10^9/L Step 2: Convert this value to cells per 10^12 to subtract from the RBC count. 410 × 10^9/L = 0.41 × 10^12/L Step 3: Subtract the WBC count from the RBC count to get the accurate RBC count. 3.28 (original RBC) – 0.41 (true WBC) = 2.87 × 10^12/L = accurate RBC The Hct may be obtained by microhematocrit centrifugation. The true MCV may be obtained by using the standard formula: MCV = (Hct ÷ RBC) × 10 where RBC = RBC count in millions per microliter. Additionally, the PLT count must be verified by smear estimate or performed manually.

Answer 134

A The PLT clumping phenomenon is often induced in vitro by the anticoagulant EDTA. Redrawing a sample from the patient by using a sodium citrate tube usually corrects this phenomenon and allows for accurate PLT enumeration. The PLT count must be multiplied by 1.11 to adjust for the amount of sodium citrate. PLT clumps cause a spurious decrease in the PLT count by automated methods. The WBC value has an “R” (review) flag because the PLT clumps have been falsely counted as WBCs; therefore, a manual WBC count is indicated.

Answer 135

D The presence of high-titer cold agglutinin in a patient with cold AIHA will interfere with automated cell counting. The most remarkable findings are falsely elevated MCV, MCH, and MCHC, as well as falsely decreased RBC count. The patient’s RBCs will quickly agglutinate in vitro when exposed to ambient temperatures below body temperature. To correct for this phenomenon, the EDTA tube should be incubated at 37°C for 15 to 30 minutes, and then the specimen should be rerun.

Answer 136

C The rule of thumb regarding the Hgb/Hct correlation dictates that Hgb × 3 ≈ Hct (± 3). This rule has been violated in this patient; therefore, a follow-up verification procedure is indicated. Additionally, MCHC is markedly elevated in these results, and an explanation for falsely increased Hgb should be sought. Lipemia can be visualized by centrifuging the EDTA tube and observing for a milky white plasma. To correct for the presence of lipemia, a plasma Hgb value (baseline Hgb) should be ascertained by using the patient’s plasma and subsequently subtracted from the original falsely elevated Hgb value. The following formula can be used to correct for lipemia: Whole blood Hgb – [(Plasma Hgb) (1 – Hct/100)] = Corrected Hgb

Answer 137

C The markedly decreased WBC count (0.2 × 10^9/L) indicates that a manual differential is necessary and that very few leukocytes will be available for differential cell counting. To increase the yield and thereby facilitate counting, differential smears should be prepared by using the buffy coat technique.

Answer 138

B CLL is a disease of older adults, classically associated with an elevated WBC count and relative and absolute lymphocytosis. CLL is twice as common in men, and smudge cells (WBCs with little or no surrounding cytoplasm) are usually present in the peripheral blood smear. CLL may occur with or without anemia or thrombocytopenia. The patient’s age and lack of blasts rule out ALL. Similarly, the patient’s age and lack of atypical lymphocytes make infectious mononucleosis unlikely. Myelodysplastic syndromes may involve the erythroid, granulocytic, or megakaryocytic cell lines but not the lymphoid cells.

Answer 139

B The finding of ovalocytes as the predominant RBC morphology in peripheral blood is consistent with the diagnosis of HE, or ovalocytosis. This disorder is relatively common and can range in severity from an asymptomatic carrier state to homozygous HE with severe hemolysis. The most common clinical subtype is associated with no or minimal hemolysis. Therefore, HE is usually associated with a normal RBC histogram and cell indices and will go unnoticed without microscopic evaluation of the peripheral blood smear.

Answer 140

A The osmotic fragility test is indicated as a confirmatory test for the presence of numerous spherocytes, and individuals with HS have an increased osmotic fragility. MCHC is elevated in greater than 50% of patients with spherocytosis, and this parameter can be used as a clue to the presence of HS. Spherocytes have a decreased surface:volume ratio, probably resulting from mild cellular dehydration.

Answer 141

D β-thalassemia minor can be easily detected by noting an abnormally elevated RBC count and Hct that does not correlate with the elevated RBC count, in conjunction with a decreased MCV. Although thalassemia and IDA are both microcytic, hypochromic processes, thalassemia can be differentiated from IDA because in IDA the RBC count, Hgb, and Hct values are usually decreased along with MCV. Although the RBC count is increased in PV, Hct must also be greater than 50% for a diagnosis of PV to be considered.

Answer 142

B The findings of moderate anemia, numerous target cells seen on the peripheral blood smear, and the presence of NRBCs are often associated with hemoglobinopathies. Hgb electrophoresis at alkaline pH is a commonly performed test to correctly diagnose the type of hemoglobinopathy.

Answer 143

B In vivo, activation of coagulation occurs on the surface of activated platelets (PLTs) or cells that have TF. TF is found on the surface of many cells outside the vascular system (extrinsic). On vascular injury, TF is exposed to the vascular system. TF has high affinity for factors VII and VIIa. TF activates factor VII to VIIa and forms TF– VIIa complex. TF–VIIa complex in the presence of calcium ion (Ca2+) and PLT phospholipid activates factor IX to factor IXa and factor X to factor Xa. Factor Xa forms a complex with cofactor Va (Xa–Va) on the surface of the activated PLTs. Factor Xa–Va complex in the presence of Ca2+ and PLT phospholipid converts prothrombin (factor II) to thrombin (IIa). Thrombin acts on soluble plasma fibrinogen to form a fibrin clot, which is stabilized by activated factor XIII (XIIIa). In addition, activated factor IX (IXa) forms a complex with activated cofactor VIII (VIIIa) on the surface of the activated PLTs. Factor IXa–VIIIa complex in the presence of Ca2+ and PLT phospholipid converts factor X to Xa with the end products of thrombin and fibrin clot, as discussed previously. The classical description of intrinsic, extrinsic, and common pathways does not take place in vivo. The concept of these three pathways is used to explain clot formation in laboratory tests. Activated thromboplastin time (APTT) is determined by the intrinsic and common pathways, whereas prothrombin time (PT) is determined by the extrinsic and common pathways. The extrinsic pathway is so named because TF is derived from extravascular cells.

Answer 144

C Factor XIIa does not play a role in coagulation in vivo; however, in vitro, the deficiency of this factor causes prolonged APTT. In vitro, factor XII is activated by substances, such as glass, Kaolin, and ellagic acid, and in vivo it may be activated by exposure to a negatively charged cell surface membrane, such collagen, as well as to kallikrein and high-molecular-weight kininogen (HMWK). In vivo, factor XIIa plays an important role in the fibrinolytic system by activating plasminogen to plasmin. Plasmin degrades the fibrin clot at the site of injury. Deficiency of factor XII is associated with thrombosis and not with bleeding. Factors VIIa, Xa, and IIa play a role in vivo and in vitro.

Answer 145

B The anticoagulant of choice for most coagulation procedures is sodium citrate (3.2%). Because factors V and VIII are more labile in sodium oxalate, heparin neutralizes thrombin, and EDTA inhibits thrombin’s action on fibrinogen, these anticoagulants are not used for routine coagulation studies.

Answer 146

C The optimal anticoagulant:blood ratio is one part anticoagulant to nine parts blood. The anticoagulant supplied in this amount is sufficient to bind all the available calcium, thereby preventing clotting.

Answer 147

A The volume of blood in a polycythemic patient contains so little plasma that excess anticoagulant remains and is available to bind to reagent calcium, thereby resulting in prolongation of PT and APTT. For more accurate results, the plasma:anticoagulant ratio can be modified by decreasing the amount of anticoagulant in the collection tube by using the following formula: (0.00185)(V)(100–H) = C, where V = blood volume in milliliters (mL); H = patient’s hematocrit (Hct); and C = volume (mL) of anticoagulant. A new sample should be drawn to rerun the PT and APTT tests.

Answer 148

C Thromboplastin and calcium (combined into a single reagent) replace tissue thromboplastin and calcium necessary, in vivo, to activate factor VII to factor VIIa. This ultimately generates thrombin from prothrombin via the coagulation cascade.

Answer 149

C Factor X is involved in the common pathway of the coagulation cascade; therefore, its deficiency prolongs both PT and APTT. Activated factor X along with activated factor V in the presence of calcium and platelet factor 3 (PF3) converts prothrombin (factor II) to the active enzyme thrombin (factor IIa).

Answer 150

D Factor XIII is not measured by PT or APTT. Factor XIII (fibrin stabilizing factor) is a transamidase. It creates covalent bonds between fibrin monomers, which are formed during the coagulation process, to produce a stable fibrin clot. In the absence of factor XIII, the hydrogen bonded fibrin polymers are unstable and, therefore, soluble in 5M urea or in 1% monochloroacetic acid.

Answer 151

C Fibrinogen can be quantitatively measured by modification of the TT by diluting the plasma because the thrombin clotting time of diluted plasma is inversely proportional to the concentration of fibrinogen (principle of Clauss method)

Answer 152

C Vitamin K is necessary for activation of vitamin K–dependent clotting factors (II, VII, IX, and X). This activation is accomplished by carboxylation of glutamic acid residues of the inactive clotting factors. The activity of vitamin K is not enhanced by heparin therapy. Vitamin K is present in a variety of foods and is also the only vitamin made by the organisms living in the intestine.

Answer 153

D D-dimer is a specific product resulting from digestion of cross-linked fibrin only. It consists of two D domains called D-D fragment and is a marker for thrombosis and fibrinolysis. In the D-dimer test, monoclonal antibody is directed against D-dimer antigen by using a variety of automated instruments. The D-dimer test is used to diagnose acute and chronic disseminated intravascular coagulation (DIC) and to rule out thromboembolic disorders. Fragments X, Y, D, and E are produced by the action of plasmin on fibrinogen and fibrin. Polypeptide A and B are produced by the proteolytic action of thrombin on fibrinogen to form a fibrin clot.

Answer 154

C The APTT test evaluates the clotting factors in the intrinsic pathway (XII, XI, IX, and VIII) as well as those in the common pathway (X, V, II, and I).

Answer 155

B Patients with vitamin K deficiency exhibit decreased production of functional prothrombin proteins (factors II, VII, IX, and X). Decreased levels of these factors prolong both PT and APTT.

Answer 156

B INR is used to standardize PT results to adjust for the differences in thromboplastin reagents made by different manufacturers and used by various institutions. The INR calculation uses the international sensitivity index (ISI) value and is used to monitor an oral anticoagulant, such as warfarin. INR is not used to standardize APTT testing.

Answer 157

C tPA is an endogenous (produced in the body) activator of plasminogen. It is released from the endothelial cells by the action of protein C. It converts plasminogen to plasmin. Streptokinase is an exogenous (not made in the body) activator of plasminogen.

Answer 158

C α2-Antiplasmin is the main inhibitor of plasmin. It inhibits plasmin by forming a 1:1 stoichiometric complex with any free plasmin in plasma and, thus, prevents binding of plasmin to fibrin and fibrinogen

Answer 159

D The D-dimer assay evaluates fibrin degradation. It is a nonspecific screening test that shows increased values in many conditions in which fibrinolysis is increased, such as DIC and fibrinolytic therapy. The D-dimer test is widely used to rule out thrombosis and thrombotic activities. The negative predictive value of a test is the probability that a person with a negative result is free of the disease that the test is meant to detect. Therefore, a negative D-dimer test result rules out thrombosis, and further laboratory investigations are not required

Answer 160

A Factor I (fibrinogen), along with the glycoprotein IIb–IIIa complex, is necessary for PLT aggregation. Factor I is also a substrate in the common pathway of coagulation. Thrombin acts on fibrinogen to form fibrin clots.

Answer 161

B A 4.5-mL blue-top tube contains 4.5 mL blood + 0.5 mL sodium citrate. The tube should be 90% full. A tube with 3.0 mL blood should be rejected because the quantity is not sufficient (QNS). QNS samples alter the necessary blood:anticoagulant ratio (9:1). The excess anticoagulant in a QNS sample binds to the reagent calcium, resulting in prolongation of PT and APTT

Answer 162

A According to Clinical Laboratory Standards Institute (CLSI) guidelines, plasma samples for PT testing, if capped, are stable for 24 hours at room temperature. Refrigerating the sample causes cold activation of factor VII and, therefore, shortened PT results. APTT samples are stable for 4 hours if stored at 4°C.

Answer 163

B Primary fibrinolysis is a rare pathological condition in which spontaneous systemic fibrinolysis occurs. Plasmin is formed in the absence of coagulation activation and clot formation. Primary fibrinolysis is associated with increased production of plasminogen and plasmin, decreased plasmin removal from the circulation, and spontaneous bleeding.

Answer 164

B Plasminogen deficiency is associated with thrombosis. Plasminogen is an important component of the fibrinolytic system. Plasminogen is activated to plasmin, which is necessary for the degradation of fibrin clots to prevent thrombosis. When plasminogen is deficient, plasmin is not formed, causing a defect in the clot lysing processes.

Answer 165

D Factors V and VIII are activated by the thrombin that is generated by the action of TF-VIIa on factor X to form factor Xa. Factor Xa forms a complex with factor Va on the PLT surfaces. Factor Xa–Va complex in the presence of phospholipid and Ca2+ transform more prothrombin to thrombin.

Answer 166

A The chromogenic, or amidolytic, assays use a color-producing substance, known as chromophore. The chromophore used for the coagulation laboratory is pNa. pNa is bound to a synthetic oligopeptide substrate. The protease cleaves the chromogenic substrate at the site binding the oligopeptide to the pNa, which results in release of pNa. Free pNa has a yellow color; the color intensity of the solution is proportional to protease activity and is measured by a photodetector at 405 nm.

Answer 167

D The D-dimer is the fibrin degradation product generated by the action of plasmin on cross-linked fibrin formed by XIIIa. The patient’s plasma is mixed with latex particles coated with monoclonal antibodies against D-domains. The test can be automated, or performed manually on a glass slide by looking macroscopically for agglutination. Enzyme-linked immunosorbent assay (ELISA) methods are also available. Normal D- dimer in plasma is less than 2 ng/mL. Increased levels of D-dimer are associated with DIC, thrombolytic therapy, venous thrombosis, and thromboembolic disorders. The D- dimer assay has a 90% to 95% negative predictive value and has been used to rule out thrombosis and thromboembolic disorders.

Answer 168

B TTP is a quantitative PLT disorder associated with increased intravascular PLT activation and aggregation resulting in thrombocytopenia. PT and APTT results are normal in TTP.

Answer 169

B Hypersplenism is associated with thrombocytopenia. In this condition, up to 90% of PLTs can be sequestered in the spleen, causing decreases in circulatory PLTs. Splenectomy, acute blood loss, and increased proliferation of pluripotent stem cells are associated with thrombocytosis

Answer 170

B Aspirin prevents PLT aggregation by inhibiting the activity of the enzyme cyclo- oxygenase. This inhibition prevents the formation of TXA2, which serves as a potent PLT aggregator.

Answer 171

B Glycoprotein Ib is a PLT receptor for VWF. Glycoprotein Ib and VWF are both necessary for a normal PLT adhesion. Other proteins that play a role in PLT adhesion are glycoproteins V and IX.

Answer 172

C Von Willebrand disease is an inherited, qualitative PLT disorder that results in increased bleeding, prolonged APTT, and decreased factor VIII:C and VWF levels. The PLT count and morphology are generally normal in von Willebrand disease, but PLT aggregation in the PLT function assay is abnormal.

Answer 173

C Bernard–Soulier syndrome is associated with thrombocytopenia and giant PLTs. It is a qualitative PLT disorder caused by the deficiency of glycoprotein Ib. In Bernard– Soulier syndrome, PLT aggregation in the PLT function assay is abnormal. Factor VIII and IX assays are not indicated for this diagnosis

Answer 174

B Bernard–Soulier syndrome is a disorder of PLT adhesion caused by deficiency of glycoprotein Ib. PLT aggregation is normal in response to collagen, ADP, and EPI but abnormal in response to ristocetin

Answer 175

C Glanzmann thrombasthenia is a disorder of PLT aggregation. PLT aggregation is normal in response to ristocetin, but abnormal in response to collagen, ADP, and EPI.

Answer 176

A Acute immune thrombocytopenic purpura is an immune-mediated disorder found predominantly in children. It is commonly associated with infection (primarily viral). It is characterized by abrupt onset, and spontaneous remission usually occurs within several weeks.

Answer 177

A TTP is a PLT disorder in which PLT aggregation increases, resulting in thrombocytopenia. Schistocytes are present in TTP as a result of microangiopathic hemolytic anemia (MAHA); however, the PT and APTT are both normal. In DIC, the PT and APTT are both prolonged, the PLT count is decreased, and schistocytes are seen in the peripheral blood smear.

Answer 178

C Neonatal alloimmune thrombocytopenia is similar to the hemolytic disease of the fetus and newborn. It results from immunization of the mother by fetal PLT antigens. The offending antibodies are commonly anti-PLT antigen A1 (PlA1), also referred to as human platelet antigen (HPA) 1a. These alloantibodies are directed against glycoproteins IIb/IIIa, Ib/IX, Ia/IIb, and CD 109. Maternal antibodies cross the placenta, resulting in thrombocytopenia in the fetus.

Answer 179

B PTP is a rare form of alloimmune thrombocytopenia characterized by severe thrombocytopenia occurring after transfusion of blood or blood products. PTP is caused by antibody-related PLT destruction in previously immunized patients. In the majority of cases, the alloantibody produced is against PlA1 (HPA-1a).

Answer 180

C HUS is caused by E. coli 0157:H7. It is associated with ingestion of E. coli– contaminated foods and is commonly seen in children. The clinical manifestations in HUS are fever, diarrhea, thrombocytopenia, MAHA, and renal failure.

Answer 181

C Storage pool deficiencies are defects of PLT granules. Most commonly, a decrease in PLT-dense granules is present with decreased release of ADP, ATP, calcium, and serotonin from PLT-dense granules

Answer 182

B Lumi-aggregation measures PLT aggregation and ATP release. It is performed on whole blood diluted with saline. PLT aggregation is measured by impedance, whereas ATP release is measured by addition of luciferin to a blood sample. There is no ATP release in storage pool deficiencies.

Answer 183

B TTP is characterized by neurological problems, fever, thrombocytopenia, MAHA, and renal failure

Answer 184

A Acquired TTP is an autoimmune disease associated with autoantibodies produced against VWF cleaving enzyme (ADAMTS-13). This deficiency results in an increase in plasma VWF and consequently increased PLT aggregation and thrombocytopenia.

Answer 185

D Hereditary hemorrhagic telangiectasia (Osler–Weber–Rendu syndrome) is a connective tissue disorder associated with telangiectases (dilated capillaries) of the mucous membranes and skin. Lesions may develop on the tongue, lips, palate, face, hands, and nasal mucosa and throughout the gastrointestinal tract. This disorder is an autosomal dominant condition that usually manifests in adolescence or early adulthood.

Answer 186

C Prostacyclin is released from the endothelium and is an inhibitor of PLT aggregation. TXA2 promotes PLT aggregation. Thromboxane B2 is an oxidized form of TXA2 and is excreted in urine. AT is a physiological anticoagulant

Answer 187

C Gray syndrome is a PLT granule defect associated with a decrease in alpha granules resulting in decreased production of alpha granule proteins, such as PF4 and beta thromboglobulin. Alpha granule deficiency results in the appearance of agranular PLTs when viewed in a Wright-stained blood smear

Answer 188

D The VerifyNow P2Y12 test is used to assess a patient’s response to antiplatelet drugs, such as clopidogrel (Plavix) and prasugrel (Effient). These drugs are given orally along with aspirin for prevention of thrombosis or as alternative antiplatelet drugs for patients who cannot tolerate or are not sensitive to aspirin. Clopidogrel and prasugrel prevent PLT aggregation by irreversibly binding to P2Y12, which is a PLT membrane receptor for ADP. The VerifyNow P2Y12 test is a whole blood test and uses ADP as an aggregating agent to measure the level of PLT aggregation impaired by these medications. The baseline value for PLT aggregation is established. The percent (%) change from baseline aggregation is calculated and reported as % P2Y12 inhibition.

Answer 189

D All of the instruments listed can be used to evaluate PLT function. PLT function testing is done either to determine the cause of bleeding in a patient with normal PLT count and normal coagulation tests or to assess the efficacy of antiplatelet drugs. PLT aggregometry is used for the diagnosis of inherited PLT disorders. A PLT aggregometer uses PLT-rich plasma to measure PLT aggregation in response to different PLT aggregating agents by measuring light transmission. A Lumi- aggregometer uses whole blood and has the ability to measure dense-granule secretion (by using a luminescent marker) in addition to PLT aggregation. The VerifyNow measures a patient’s response to multiple antiplatelet drugs, including aspirin, P2Y12 inhibitors, and glycoprotein IIb/IIIa inhibitors. The Platelet Function Ananlyzer-100 (PFA-100) is used as a screening tool for PLT function, and has replaced the bleeding time test. It uses citrated whole blood and two cartridges. Whole blood (800 μL) is put into each test cartridge. Vacuum is used to move the blood through a very thin glass tube that has been coated with a membrane containing collagen and either EPI or ADP. This coating activates the PLTs in the moving sample and promotes PLT adhesion and aggregation. The time it takes for the clot to form inside the glass tube and prevent further flow is measured as the closure time (CT). Initial screening is done with collagen/EPI. If CT is normal, it is unlikely that PLT dysfunction exists. The collagen/ADP membrane is used to confirm an abnormal collagen/EPI test result. If both tests show abnormal results, it is likely that the patient has a PLT dysfunction, and further testing for inherited and acquired bleeding disorders is indicated. If collagen/ADP is normal, then the abnormal collagen/EPI test result is likely caused by aspirin sensitivity.

Answer 190

B Collagen is the only commonly used agent that demonstrates a single-wave (monophasic) response preceded by a lag time.

Answer 191

B The APTT is sensitive to the deficiency of coagulation factors in the intrinsic pathway (factors XII, XI, IX, and VIII) and the common pathway (factors X, V, II, and I).

Answer 192

D The level of plasma fibrinogen determined immunologically is normal. In a patient with dysfibrinogenemia, fibrinogen is not polymerized properly, causing abnormal results of the fibrinogen-dependent coagulation tests.

Answer 193

D Obstructive jaundice contributes to coagulation disorders by preventing vitamin K absorption. Vitamin K is fat soluble and requires bile salts for absorption. Parenteral administration of vitamin K bypasses the bowel, hence the need for bile salts.

Answer 194

A Factor X, a common pathway factor deficiency, is most likely suspected because both PT and APTT are prolonged. Other causes may include liver disease, vitamin K deficiency, and anticoagulant drugs, such as warfarin and heparin.

Answer 195

C Because prolonged APTT is not corrected with factor IX–deficient plasma, factor IX is suspected to be deficient in the test plasma.

Answer 196

C Hemophilia A (factor VIII deficiency) is characterized by mild to severe bleeding episodes, depending on the concentration of factor VIII:C. Hemophilia A is inherited as a sex-linked disease. PLT aggregation and PT are both normal in hemophilia A

Answer 197

C In DIC, there is a diffuse intravascular generation of thrombin and fibrin. As a result, clotting factors and PLTs are consumed, resulting in decreased PLT count and increased PT and APTT.

Answer 198

A Adenocarcinoma can liberate procoagulant (thromboplastic) substances that can activate prothrombin intravascularly. ITP is a thrombocytopenia caused by an autoantibody; PTP is an alloimmune thrombocytopenia caused by transfusion of blood or blood products; HIT results from an antibody to heparin–PF4 complex causing thrombocytopenia in 1% to 5% of patients who are on heparin therapy. In some affected persons, thrombosis may also occur

Answer 199

D Factor XII–deficient patients commonly have thrombotic episodes. In vitro, activated factor XII (XIIa) activates factor XI to factor XIa. In vivo, however, factor XII plays a major role in the fibrinolytic system by activating plasminogen to form plasmin. Hemorrhagic manifestations are not associated with factor XII deficiency because VIIa/TF can activate factor IX to factor IXa and factor X to factor Xa to generate thrombin.

Answer 200

A Hemophilia A is associated with deficiency of factor VIII, resulting in bleeding and abnormal APTT. The PLT number and function are normal in this disorder. Von Willebrand disease is a disorder of PLT adhesion associated with decreased VWF and factor VIII, causing an abnormal PLT function test result and abnormal APTT. Both Glanzmann thrombasthenia and Bernard–Soulier syndrome cause abnormal PLT aggregation but do not cause abnormal APTT.

Answer 201

D Fibrinogen (factor I) is a clotting protein of the common pathway and is evaluated by TT. In hypofibrinogenemia (fibrinogen concentration less than 100 mg/dL), PT, APTT, and TT are prolonged. In factor VII deficiency, APTT is normal; in factor VIII deficiency, PT is normal; and in factor X deficiency, TT is normal.

Answer 202

B Coagulation factor assays are based on the ability of the patient’s plasma to correct any specific factor–deficient plasma. To measure for factor VIII activity in a patient’s plasma, diluted patient plasma is mixed with factor VIII–deficient plasma. The APTT test is performed on the mixture. Each laboratory should calculate its own normal ranges, which are based on the patient population, reagents, and instrument used. A range of 50% to 150% is considered normal.

Answer 203

B Factor VIII concentrate (human or recombinant) is the treatment of choice for patients with factor VIII deficiency. FFP contains factor VIII; however, it is no longer used as the primary treatment for factor VIII deficiency. Prothrombin complex concentrate is used to treat patients with factor VIII inhibitor.

Answer 204

D Fibrinogen is a plasma protein that is essential for PLT aggregation as well as fibrin formation. In afibrinogenemia, PLT aggregation is abnormal.

Answer 205

C VWF is involved in both PLT adhesion and coagulation via complexing with factor VIII. Therefore, in von Willebrand disease (deficiency or functional abnormality of VWF) factor VIII is also decreased, causing abnormal APTT as well as abnormal PLT aggregation to ristocetin. The PLT count and PT are not affected in VWF deficiency

Answer 206

A Hemophilia A is associated with factor VIII deficiency. Factor VIII is a factor in the intrinsic coagulation pathway that is evaluated by the APTT test and not the PT test. The PT test evaluates the extrinsic and common pathways.

Answer 207

B Increased fibrin monomers result from coagulation activation. DIC is an acquired condition associated with spontaneous activation of coagulation and fibrinolysis. In primary fibrinolysis, the fibrinolytic system is activated, and fibrin monomers are normal.

Answer 208

B Most of the clotting factors are made in the liver. Therefore, severe liver disease results in multiple-factor deficiencies. An inherited disorder of coagulation is commonly associated with a single-factor deficiency. Lupus anticoagulant is directed against the phospholipid-dependent coagulation factors. Dysfibrinogenemia results from an abnormal fibrinogen molecule.

Answer 209

D Factor XIII deficiency can lead to impaired wound healing and may cause severe bleeding problems. Factor XIII is a fibrin stabilizing factor that changes the fibrinogen bonds in fibrin polymers to stable covalent bonds. Factor XIII is not involved in the process of fibrin formation and, therefore, PT and APTT are both normal.

Answer 210

B Fletcher factor (prekallikrein) is referred to as a contact factor. Activated prekallikrein is named kallikrein. In vitro, kallikrein is involved in activation of factor XI to XIa causing prolonged APTT. In vivo, it plays a role in the fibrinolytic system and, similar to factor XII deficiency, Fletcher factor deficiency may be associated with thrombosis.

Answer 211

A In severe hemophilia A, factor VIII activity is less than 1%, resulting in a severe bleeding diathesis, such as hemarthrosis (bleeding into the joints).

Answer 212

A VWF is a multimeric plasma glycoprotein that results in different subtypes of von Willebrand disease with varied severity. The most common subtype is subtype 1, and 70% to 80% of these cases are associated with mild bleeding. Subtype 3 involves the total absence of the von Willebrand molecule and is associated with severe bleeding. Subtypes 2A and 2B result in deficiency of intermediate- and/or high-molecular- weight portions of the von Willebrand molecule and are associated with 10% to 12% and 3% to 6% of cases of von Willebrand disease, respectively

Answer 213

B Factor V (common pathway factor) deficiency is most likely suspected because both PT and APTT are prolonged, and both are corrected when mixed with normal plasma.

Answer 214

C AT is a heparin cofactor and is the most important naturally occurring physiological inhibitor of blood coagulation. It represents about 75% of antithrombotic activity and is an α2-globulin made by the liver.

Answer 215

A Heparin is an AT drug and therefore increases TT along with APTT and PT. Heparin therapy has no effect on fibrinogen, protein C, or protein S assays

Answer 216

D In the presence of a pathological circulating anticoagulant, a mixing test using normal plasma does not correct abnormal APTT. These anticoagulants are pathological substances and are endogenously produced. They are either directed against a specific clotting factor or against a group of factors. Prolonged APTT caused by a factor deficiency is corrected when mixed with normal plasma. Factors VIII– and factor IX– deficient plasmas are used for assaying the activities of factors VIII and IX, respectively

Answer 217

D The lupus anticoagulant interferes with phospholipid-dependent coagulation assays, such as the PT and APTT tests. The lupus anticoagulant does not inhibit clotting factor assays and does not inhibit in vivo coagulation.

Answer 218

B Warfarin (Coumadin) crosses the placenta and is present in human milk; it is not recommended for pregnant and lactating women. Warfarin is a vitamin K antagonist drug that retards synthesis of the active form of vitamin K–dependent factors (II, VII, IX, and X). AT is a heparin (not warfarin) cofactor. The INR is used to monitor warfarin dosage.

Answer 219

D Protein S functions as a cofactor of protein C and, as such, enhances its activity. Activated protein C (APC) inactivates factors Va and VIIIa.

Answer 220

B Russell viper venom (RVV) reagent contains factors X and V, activating enzymes that are strongly phospholipid dependent. The reagent also contains RVV, Ca2+, and phospholipid. In the presence of phospholipid autoantibodies, such as lupus anticoagulant, the reagent phospholipid is partially neutralized, causing prolongation of clotting time. TT evaluates fibrinogen. D-dimer tests evaluate fibrin degradation products. Fibrinogen assay and TT are not indicated for the diagnosis of lupus anticoagulant.

Answer 221

B APCR is the single most common cause of inherited thrombosis. In 90% of individuals, the cause is gene mutation of factor V (factor V Leiden). Affected individuals are predisposed to thrombosis, mainly after age 40 years. Heterozygous individuals may not manifest thrombosis unless other clinical conditions coexist.

Answer 222

D Heparin is a therapeutic anticoagulant with an AT activity. Heparin also inhibits factors XIIa, XIa, Xa, and IXa. In patients receiving heparin therapy, PT, APTT, and TT are all prolonged. Quantitative fibrinogen assay, however, is not affected by heparin therapy.

Answer 223

D Prasugrel (Effient) is an antiplatelet drug that reduces PLT aggregation by irreversibly blocking P2Y12 receptors on the PLT surface membrane, thereby inhibiting PLT aggregation to ADP. Aspirin is another antiplatelet drug that inhibits PLT aggregation by blocking the action of the enzyme cyclo-oxygenase. Warfarin and heparin are anticoagulant drugs that act against clotting factors.

Answer 224

A Protein C is activated by thrombin–TM complex. TM is a transmembrane protein that accelerates protein C activation 1,000-fold by forming a complex with thrombin. When thrombin binds to TM, it loses its clotting function, including activation of factors V and VIII. APC deactivates factors Va and VIIIa. Protein S is a cofactor necessary for the activation of protein C.

Answer 225

B Heparin dosage can be best monitored by the chromogenic anti–factor Xa assay. In anti–factor Xa assay, the concentration of heparin is determined by inhibition of factor Xa by AT. Anti–factor Xa assay uses a reagent with a fixed concentration of factor Xa and AT. Heparin forms a complex with AT and factor Xa reagents. Excess factor Xa combines with the chromogenic substrate to form a colored product; the color intensity is inversely proportional to the concentration of heparin. PT would be prolonged in heparin therapy, but the PT test is not sensitive enough to be used to monitor heparin therapy. Heparin inhibits thrombin and, therefore, causes prolonged TT. The TT test, however, is not used to monitor heparin therapy either.

Answer 226

A Warfarin is a vitamin K–antagonist drug. It inhibits vitamin K–dependent factors (II, VII, IX, and X) and other vitamin K–dependent proteins, such as proteins C and S. Warfarin therapy is monitored with the INR. An INR of 2.0 to 3.0 is used as the target when monitoring warfarin therapy for prophylaxis and treatment of deep vein thrombosis (DVT). A higher dose of warfarin (giving an INR of 2.5–3.5) is required for patients with mechanical heart valves

Answer 227

B Factors Va and VIIIa are deactivated by protein S and activated by protein C.

Answer 228

C Urokinase is a thrombolytic drug that can be used to treat acute arterial thrombosis. Urokinase can also be used for the treatment of venous thromboembolism, myocardial infarction, and clotted catheters. Warfarin and heparin are anticoagulant drugs, whereas aspirin prevents PLT aggregation by inhibiting cyclo-oxygenase.

Answer 229

C The International Society of Hemostasis and Thrombosis has recommended four criteria for the diagnosis of lupus anticoagulant: (1) prolongation of one or more of the phospholipid-dependent clotting tests, such as APTT or DRVVT; (2) presence of an inhibitor confirmed by mixing studies (not corrected); (3) evidence that the inhibitor is directed against phospholipids by neutralizing the antibodies with a high concentration of phospholipids (PLT neutralization test or DRVVT with platelet rich plasma or confirming phospholipid reagent); and (4) lack of any other causes for thrombosis

Answer 230

B Lupus anticoagulant interferes with phospholipids in the APTT reagent, resulting in prolongation of APTT. However, in vivo, lupus anticoagulant decreases fibrinolytic activity, causing an increased risk of thrombosis. Lupus anticoagulant does not result in a bleeding tendency unless there is a coexisting thrombocytopenia or other coagulation abnormality.

Answer 231

C LMWH is a small glycosaminoglycan that is derived from UFH. LMWH has a low affinity for plasma proteins and endothelial cells and therefore has a longer half-life. The half-life of the drug does not depend on the dosage. LMWH has an inhibitory effect on factors Xa and IIa. It does not require routine monitoring except in patients with renal failure, obese patients, pediatric patients, and pregnant patients.

Answer 232

C Aspirin is an antiplatelet drug. It prevents PLT aggregation by inhibition of cyclo- oxygenase. Aspirin has no effect on the PLT count, PLT morphology, or PT.

Answer 233

B AT is a physiological anticoagulant. It inhibits factors IIa, Xa, IXa, XIa, and XIIa. Deficiency of AT is associated with thrombosis. Thrombotic events commonly occur when AT deficiency is associated with another risk factor, such as pregnancy, surgery, or an inherited thrombotic disorder (e.g., factor V Leiden)

Answer 234

A Protein C is a physiological inhibitor of coagulation. It is activated by thrombin–TM complex. APC inhibits cofactors Va and VIIIa. Protein C deficiency is associated with thrombosis. Increased fibrinolysis, afibrinogenemia, and ITP are associated with bleeding.

Answer 235

C Up to 22% of patients taking aspirin become resistant to aspirin’s antiplatelet effect. Patients who are aspirin resistant have a higher risk of thrombosis (heart attacks and strokes).

Answer 236

D Heparin is an AT drug causing prolonged TT in patients who are on heparin therapy. Prasugrel, clopidogrel, and aspirin are antiplatelet drugs causing inhibition of PLT aggregation.

Answer 237

C Laboratory tests for evaluation of thrombophilia are justified in young patients with thrombotic events, in patients with a positive family history after a single thrombotic event, in those with recurrent spontaneous thrombosis, and in pregnancies associated with thrombosis.

Answer 238

B Prothrombin G20210A is defined as a single-point mutation of the prothrombin gene, resulting in increased concentration of plasma prothrombin and, thus, is a risk factor for thrombosis. Prothrombin G20210A is the second most common cause of inherited hypercoagulability (after factor V Leiden). It has the highest incidence in white people from southern Europe. The thrombotic episodes generally occur before age 40 years.

Answer 239

A Factor V Leiden is a single-point mutation in the factor V gene that inhibits factor Va inactivation by protein C. APC enhances deactivation of factors Va and VIIIa.

Answer 240

B The incidence of antiphospholipid antibodies in the general population is about 1% to 2%.

Answer 241

D Currently, the PLT aggregation test is considered the gold standard for evaluation of aspirin resistance. In aspirin resistance, PLT aggregation is not inhibited by aspirin ingestion. Aspirin resistance has no effect on PLT count and morphology

Answer 242

B TFPI is released from the vasculature and is the most important inhibitor of the extrinsic pathway. TFPI inhibits factors Xa and VIIa–TF complex. Therefore, the deficiency of TFPI is associated with thrombosis.

Answer 243

D Factor VIII inhibitors (alloantibodies) occur in 20% to 25% of patients who have factor VIII deficiency and are receiving factor VIII replacement

Answer 244

B rVIIa is effective for the treatment of a high-titer factor VIII inhibitor. Factor VIIa can directly activate factor X to factor Xa in the absence of factors VIII and IX. rVIIa does not stimulate anamnestic responses in patients with factor VIII inhibitor. Factor VIII concentrate is used for a low-titer factor VIII inhibitor. Factor X concentrate and FFP are not the treatments of choice for factor VIII inhibitor.

Answer 245

B The Bethesda assay is a quantitative assay for factor VIII inhibitor. In this assay, normal plasma is incubated with different dilutions of the patient’s plasma or with a normal control. The inhibitor inactivates factor VIII present in normal plasma following incubation for 2 hours at 37°C. The residual activities in the sample are determined, and the inhibitor titer is calculated.

Answer 246

C Elevated plasma homocysteine is a risk factor for the development of DVT, coronary heart disease and stroke. Homocystinemia may be inherited or acquired. Acquired homocystinemia is caused by dietary deficiencies of vitamins B6, B12, and folic acid.

Answer 247

C Oral contraceptive drugs are acquired risk factors for thrombosis. Aspirin and clopidogrel are antiplatelet drugs, and tPA is a fibrinolytic drug used for the treatment of thrombosis.

Answer 248

A Argatroban is a direct thrombin-inhibiting drug and may be used as an anticoagulant in patients with HIT to prevent thrombosis. Argatroban is a small synthetic molecule that binds to free and clot-bound thrombin. Argatroban affects TT, PT, APTT, and activated clotting time (ACT) tests. The APTT test is recommended for monitoring the dosage with the target therapeutic range of 1.5 to 3.0 times the mean of the laboratory reference range. In patients with lupus anticoagulant or factor deficiencies, baseline APTT is prolonged; in these conditions, Ecarin time can be used as an alternative assay.

Answer 249

D HIT is an immune process caused by the production of antibodies to heparin–PF4 complex. This immune complex binds to PLT Fc receptors, causing PLT activation and formation of PLT microparticles, which, in turn, induce hypercoagulability and thrombocytopenia

Answer 250

C APCR can be evaluated by performing a two-part APTT test. The APTT is measured on the patient’s plasma with and without the addition of APC. The result is expressed as the ratio of the APTT with APC to the APTT without APC. The normal ratio is 2:5. Patients with APCR have a lower ratio than the reference range. A positive screening test should be followed by a confirmatory test, such as polymerase chain reaction (PCR) for factor V Leiden.

Answer 251

D Ecarin clotting time, a snake venom–based clotting assay, may be used to monitor bivalirudin therapy in instances when the baseline APTT is prolonged as a result of lupus anticoagulant or factor deficiencies. Heparin therapy is monitored by using the anti–factor Xa assay; warfarin therapy is monitored with the INR. Fibrinolytic therapy may be monitored by using the D-dimer test

Answer 252

A The lupus anticoagulant interferes with the APCR screening assay based on the APTT ratio with and without the addition of APC. Persons with the lupus anticoagulant have a prolonged APTT that renders the test invalid for APCR screening

Answer 253

D Hyperfibrinogenemia is a risk factor for thrombophilia. Fibrinogen is an acute-phase reactant and may be increased in inflammation, stress, obesity, smoking, and medications, such as oral contraceptives. Hypofibrinogenemia, afibrinogenemia, and factor VIII inhibitors are associated with bleeding.

Answer 254

D Argatroban is a direct thrombin inhibitor drug and used in patients with HIT who cannot tolerate heparin or LMWH therapy. Warfarin should not be used for anticoagulation in persons with HIT because it causes a fall in protein C concentration and vitamin K–dependent coagulation factors. Aspirin is an antiplatelet drug.

Answer 255

B ACT is a point-of-care coagulation test used to monitor high-dose heparin therapy during cardiac surgery, cardiac angioplasty, hemodialysis, and other major surgeries. It is the preferred method to determine if sufficient heparin was administered to prevent clotting during surgery because it is more rapid than the APTT test. The test uses a clot activator, such as kaolin or Celite, to stimulate coagulation, and the time in seconds is linearly related to the dose of heparin administered. The ACT test is available in different formats, and the reference range varies, depending on the method used. At low to moderate heparin doses, the ACT test does not correlate well with the APTT test or the anti–factor Xa assay

Answer 256

C Mixing studies differentiate factor deficiencies from factor inhibitors. Lupus anticoagulant is associated with thrombosis, and it is directed against phospholipid- dependent coagulation tests, such as the APTT test. In patients with lupus anticoagulant, after the patient’s plasma is mixed with normal plasma, APTT remains prolonged immediately after mixing and following 2 hours of incubation. Factor VIII deficiency and factor VIII inhibitor are associated with bleeding

Answer 257

C The anti–factor Xa heparin assay is used to monitor LMWH therapy, when required, because the APTT test is insensitive to LMWH. The assay can be performed by chromogenic endpoint detection used on automated analyzers. The principle of the test is to measure the inhibition of factor Xa by heparin. The reagent is a mixture of a fixed concentration of factor Xa, a substrate which is specific for factor Xa, and a fixed concentration of AT. Some kits rely on the AT in the patient’s plasma. Heparin forms a complex with AT and factor Xa (AT–heparin–factor Xa). Excess free factor Xa cleaves the chromogenic substrate and releases a yellow product. The color intensity of the product is inversely proportional to plasma heparin concentration and is measured by a photodetector at 405 nm. LMWH therapy usually does not require monitoring; however, exceptions include pediatric, obese, and pregnant patients and those with renal failure.

Answer 258

C These clinical manifestations and laboratory results are consistent with ITP. ITP is an autoimmune thrombocytopenia. In children, acute ITP occurs after a viral infection, as was the case in this 3-year-old patient. Clinical manifestations are associated with petechiae, purpura, and mucous membrane bleeding, such as epistaxis and gingival bleeding. Abnormal laboratory tests include a very low PLT count, and other causes of thrombocytopenia should be ruled out in patients with suspected ITP.

Answer 259

B These clinical manifestations and laboratory results are consistent with von Willebrand disease. von Willebrand disease is an inherited bleeding disorder caused by abnormal PLT adhesion and aggregation. In von Willebrand disease, VWF is deficient or dysfunctional. VWF enhances the release of factor VIII from the liver, and it also forms a complex with factor VIII in the circulation. Deficient or dysfunctional VWF results in decreased factor VIII as well and, therefore, an increase in APTT values. The clinical manifestations associated with von Willebrand disease are easy bruising, epistaxis, and bleeding after surgery. The diagnostic laboratory test shows abnormal PLT aggregation to ristocetin, which is corrected by addition of normal plasma containing VWF. APTT is prolonged as a result of the deficiency of factor VIII. Factor VIII activity (VIII:C), VWF ristocetin cofactor activity (VWF:Rco), and VWF: antigenic activity (VWF:antigen) are abnormal. The PLT count and PT are normal in von Willebrand disease.

Answer 260

D Cryoprecipitate contains fibrinogen, factor VIII, and VWF. FFP has all of the clotting factors; however, it is not the best choice if cryoprecipitate is available.

Answer 261

C The PLT count should be checked every other day in patients receiving heparin therapy. HIT should be suspected in patients who are not responding to heparin therapy and/or are developing thrombocytopenia (50% below the baseline value) and thrombotic complications while on heparin therapy. Increase in heparin dose should be avoided in patients with the clinical symptoms of thrombosis while they are receiving heparin. Fibrinogen assay and PT are not the appropriate assays for monitoring heparin therapy, nor are they used to test for HIT

Answer 262

D Factor VIII inhibitor is found in 20% to 25% of patients with hemophilia receiving replacement therapy. It may also develop in patients with immunologic problems, women after childbirth, and patients with lymphoproliferative and plasma cell disorders, or it may develop in response to medications. Factor VIII inhibitor is an IgG with an inhibitory effect that is time and temperature dependent. The presence of factor VIII inhibitor causes elevated APTT in the face of a normal PT. Mixing studies in factors VIII and IX deficiencies will correct the prolonged APTT both at the immediate mixing stage and after incubation for 2 hours. APTT would not be corrected by mixing studies in the presence of factor VIII inhibitor. In addition, factor VIII inhibitor is associated with bleeding. Lupus anticoagulant is associated with thrombosis and not bleeding unless it coexists with thrombocytopenia, which is not the case in this patient.

Answer 263

C The clinical presentation and laboratory results in this patient are indicative of cirrhosis of the liver. Most of the clotting factors are made in the liver. A decrease in multiple clotting factors is associated with prolonged PT and APTT. Macrocytosis and target cells are present in liver disease. The liver changes the unconjugated bilirubin to conjugated bilirubin. Conjugated bilirubin is excreted into the intestines, where bilirubin is converted to urobilinogen and excreted into feces. In cirrhosis of the liver, both necrosis and obstruction caused by scarring produce increases in unconjugated and conjugated bilirubin, respectively. In addition, the liver enzymes are elevated (the AST:ALT ratio is less than 1 in necrotic liver diseases, such as hepatitis, but not in cirrhosis).

Answer 264

C Interpretation of correction studies varies among different laboratories. Some define correction when the mixing study result falls within 10% of the normal plasma; other laboratories conclude correction when the mixing result falls within 5 seconds of normal plasma, or a value within the APTT reference range. Only 50% factor activity is required for normal PT or APTT. A circulating anticoagulant typically results in failure to correct the APTT with normal plasma.

Answer 265

C A clot can form because of inadequate mixing of the sample after venipuncture, if the blood fills the evacuated tube at a slow rate, or with traumatic venipuncture. In vitro, blood clots result in consumption of the clotting factors and, therefore, prolongation of PT, APTT, and other clot-based assays. If the clotting factors have been activated but the clot formation is incomplete, it may result in shortening of PT and APTT. Checking the sample for a clot is the most reasonable step in this case.

Answer 266

B Samples for evaluation of PT are stable for 24 hours if kept at room temperature. Prolonged exposure to cold will activate factor VII, resulting in decreased PT.

Answer 267

B AT deficiency in patients receiving heparin therapy may lead to heparin resistance and, therefore, lack of prolongation of APTT. AT is a heparin cofactor and, as such, increases heparin activity by 1,000-fold. Deficiency of AT is associated with poor response to heparin therapy.

Answer 268

A Baseline PLT count and APTT should be performed on all patients prior to administration of heparin. APTT should be repeated every 4 to 6 hours after bolus injection (high dose). Response to heparin therapy varies among patients for the following reasons: heparin half-life is decreased in extended thrombosis, and the anticoagulant activities of heparin change based on nonspecific binding of heparin to plasma proteins. Therefore, heparin therapy should be closely monitored. Heparin dosage can be adjusted based on the anti–factor Xa assay. In addition, the PLT count should be monitored regularly during heparin therapy because decrease of the PLT count to 50% below the baseline value is significant and may be associated with HIT. PT is not used to monitor heparin therapy.

Answer 269

C The clinical manifestations and laboratory results in this patient are consistent with TTP. The clinical manifestations of TTP include MAHA, thrombocytopenia, fever, renal failure, and neurological symptoms. The neurological symptoms in this patient are manifested by headache, dizziness, nausea, and vomiting. Weakness and lethargy are signs and symptoms of anemia. Low Hgb and Hct with normal MCV and MCHC indicate a normocytic normochromic anemia. The presence of schistocytes in peripheral blood, with low platelet counts and low haptoglobin, are consistent with MAHA. The high BUN and creatinine levels are characteristic of renal failure. The platelet count, performed on admission, was done on a hematology analyzer and was falsely elevated because of the presence of microcytes or fragmented RBCs. The manual platelet count was much lower. The coagulation tests are normal in TTP. In von Willebrand disease, the platelet count is normal and the APTT is usually abnormal. ITP is characterized by thrombocytopenia but not hemolytic anemia (HA). DIC is associated with a low platelet count, HA, and abnormal coagulation studies. The acute onset of symptoms in this patient may be related to mitomycin used for the treatment of gastric carcinoma in this patient.

Answer 270

C These clinical manifestations and laboratory results are consistent with Glanzmann thrombasthenia. Epistaxis and easy bruising are characteristics of platelet disorders. The positive family history is indicative of an inherited bleeding disorder. Laboratory tests reveal a low Hgb level caused by epistaxis. The normal platelet count rules out any quantitative platelet disorder. The platelet count is typically low in Bernard– Soulier syndrome. Normal PT and APTT, combined with a normal factor VIII assay, rule out coagulation disorders. The laboratory tests that confirm an inherited platelet disorder are PLT aggregation studies. PLT aggregation is normal to ristocetin and abnormal to ADP, EPI, and thrombin. These results are consistent with Glanzmann thrombasthenia. PLT aggregation is abnormal to ristocetin in von Willebrand disease and Bernard–Soulier syndrome.

Answer 271

D These clinical manifestations and laboratory results are consistent with lupus anticoagulant. Pain and swelling in the patient’s right leg may be indicative of thrombosis. As many as 48% of women with repeated spontaneous abortions have lupus anticoagulant or/and antibody to phospholipid, such as anticardiolipin antibodies. The unremarkable family history in this patient rules out an inherited thrombotic disorder. Normal TT rules out fibrinogen disorders. Prolonged PT and APTT in the absence of bleeding history eliminate the diagnosis of factor deficiency. The APTT test performed on a mixture of patient plasma and normal plasma did not correct the prolonged APTT. This result is indicative of an inhibitor. However, because the patient is not bleeding, factor VIII inhibitor is not indicated. A negative anticardiolipin antibody result rules out the possibility of anticardiolipin antibodies being responsible for the patient’s clinical symptoms. The laboratory test result that confirms the presence of a lupus anticoagulant is prolonged APTT that is not corrected when mixed with normal plasma and that is neutralized by preincubation with platelet phospholipid (an excess of platelet phospholipid neutralizes the antibody, resulting in normal APTT).

Answer 272

C Performing liver biopsy in a patient with a prolonged PT and a high INR could have life-threatening consequences. In this patient, the prolonged PT is likely caused by liver disease. Vitamin K is stored in the liver and is essential for activation of factors II, VII, IX, and X. Vitamin K needs bile (secreted by the liver) for its absorption. In liver disease characterized by obstruction, bile is not secreted into the gastrointestinal tract, and therefore, vitamin K is poorly absorbed. The most logical course of action is the following: Start the patient on vitamin K therapy, repeat the PT test 4 days after starting vitamin K administration, and cancel the biopsy until the patient’s PT returns to normal.

Answer 273

B According to the CLSI guidelines, samples for APTT should be centrifuged and tested within 2 hours after collection. However, the sample is stable for 4 hours if stored at 4°C. APTT evaluates the clotting factors in the intrinsic and common coagulation pathways, including factor VIII (intrinsic) and factor V (common). Factors VIII and V are cofactors necessary for fibrin formation. However, they are both labile. Storage beyond 4 hours causes falsely elevated APTT results. The medical laboratory scientist should request a new sample for the APTT test

Answer 274

B Traditional anticoagulant drugs, such as heparin and warfarin, are well known. Newer anticoagulant drugs are available for the treatment and prevention of thrombosis. Some of these new drugs have AT or anti–factor Xa effects and, therefore, increase PT, APTT, and TT. Examples of these drugs are argatroban, which inhibits thrombin, and fondaparinux, which inhibits factor Xa.

Answer 275

C Heparin therapy should be stopped immediately when clinical symptoms indicate HIT. The blood sample should be tested at least 4 hours after heparin therapy is discontinued. Early sampling for HIT testing may give a false-negative result because of the neutralization of antibody by heparin. LMWH should not be used in patients who develop HIT because LMWH can also cause HIT. Warfarin therapy can be started in patients who respond to heparin therapy. Heparin therapy must overlap warfarin therapy until the INR reaches a stable therapeutic range (2.0–3.0). Warfarin therapy could not be used in this patient because of lack of response to heparin therapy. The first step in the treatment of HIT is discontinuation of heparin, including intravenous catheter flushes, heparin-coated indwelling catheters, UFH, and LMWH

Answer 276

B The anticoagulant:blood ratio should be adjusted for the PT and APTT tests in patients with a severe anemia. The standard anticoagulant volume (0.5 mL) is not sufficient for the large quantity of plasma in these patients, causing unreliable PT and APTT results. The low Hgb and Hct in this patient were caused by severe bleeding during surgery. To get accurate PT and APTT results, the amount of anticoagulant is adjusted according to the following formula: (0.00185)(V) (100–H) = C, where V = blood volume in mL; H = patient’s Hct; and C = volume of anticoagulant in mL. A new sample should be drawn to rerun the PT and APTT. There are other causes for decreased PT and APTT, such as increased fibrinogen and increased factor VIII; however, the preanalytical variables affecting unreliable results should be ruled out first. Heparin therapy would increase PT and APTT

Answer 277

B The absence of a positive family history in this patient indicates acquired coagulopathy. Because both the PT and APTT test results are abnormal, the clotting factor involved is most probably in the common pathway. The lack of correction by mixing studies suggests the presence of an inhibitor. Factor V antibodies are the most common antibodies among the clotting factors of the common pathway (I, II, V, and X). Factor V antibodies are reported to be associated with surgery; some antibiotics, such as streptomycin; exposure to blood products or the bovine form of “fibrin glue.” Patients with antibodies to factor V may require long-term therapy with immunosuppressive drugs. Acute bleeding episodes may be treated by platelet transfusions. The PT test is normal in patients with factor VIII deficiency and factor VIII inhibitor. Lupus anticoagulant is not present with bleeding unless associated with coexisting thrombocytopenia.

Answer 278

A The formation of plasma ultrafiltrate depends on high hydrostatic pressure and permeability of the glomeruli. Aldosterone is released when afferent arterial pressure falls, and ADH is released when plasma osmolality becomes too high. The collecting tubule reabsorbs sodium and secretes potassium in response to aldosterone and is permeable to H2O only in the presence of ADH. The thick ascending limb is permeable to salt, but not to H2O or urea.

Answer 279

A The tubules are able to concentrate the filtrate because the descending limb is highly permeable to H2O and urea, but not to salt, and the ascending limb is permeable to salt. Salt leaving the thick ascending limb creates a hypertonic interstitium that forces H2O from the descending limb. Renin is released in response to low hydrostatic pressure in the afferent arteriole, which stimulates the juxtaglomerular cells. ADH is released by the posterior pituitary in response to high plasma osmolality.

Answer 280

A Sodium is a threshold substance; that is, no sodium will be excreted in urine until the renal threshold (a plasma sodium concentration of approximately 120 mmol/L) is exceeded. Potassium is not a threshold substance and will be secreted by the tubules even when plasma potassium levels are low. Patients on diuretics or who have hypovolemia become hypokalemic for this reason. Some substances (e.g., penicillin) can be excreted at a rate exceeding glomerular filtration because the tubules secrete them. The tubules are responsible for concentrating the filtrate in conditions of water deprivation and diluting it in conditions of water excess. When tubular function is lost, salt and water equilibrate by passive diffusion, and the SG of urine becomes the same as that of plasma, approximately 1.010.

Answer 281

D Urine specimens should be plated and incubated within 2 hours of collection (some laboratories use a 1-hour time limit) and within 24 hours if the sample is refrigerated at 2°C to 8°C immediately after collection. No additives are permitted when urine is collected for culture.

Answer 282

C The first morning voided sample is the most sensitive for screening purposes because formed elements are concentrated, but random samples are satisfactory because glomerular bleeding, albuminuria, and cast formation may occur at any time. Preservative tablets should be avoided because they may cause chemical interference with some dry reagent strip and turbidimetric protein tests. Changes in glucose, bilirubin, and urobilinogen can occur within 30 minutes of collection. Therefore, samples should be refrigerated if not tested within 2 hours.

Answer 283

C Homogentisic acid causes dark brown or black-colored urine. Myoglobin causes a red to red-brown color in urine, and biliverdin causes a green or yellow-green color. In addition to metabolic diseases and renal disease, abnormal color can be caused by drugs, dyes excreted by the kidneys, and natural or artificial food coloring.

Answer 284

D Myoglobin causes a positive test for blood but does not cause urine to fluoresce. PBG causes urine to become dark (orange to orange-brown) on standing but does not fluoresce. Uroporphyrin and coproporphyrin produce red or orange-red fluorescence. Unlike hemoglobin, porphyrins lack peroxidase activity. Urobilin is an oxidation product of urobilinogen. It turns the urine orange to orange-brown but does not produce fluorescence.

Answer 285

B Lead poisoning blocks the synthesis of heme, causing accumulation of PBG and coproporphyrin III in urine. However, uroporphyrin levels are not sufficiently elevated to cause red pigmentation of urine. There is sufficient coproporphyrin to cause a positive test for fluorescence. Acute intermittent porphyria produces increased urinary delta-aminolevulinic acid (Δ-ALA), and PBG. The PBG turns urine orange to orange- brown upon standing. Erythropoietic porphyria and porphyria cutanea tarda produce large amounts of uroporphyrin, causing the urine to be red or port wine colored.

Answer 286

D Porphyria may be inherited as a result of an enzyme defect in heme synthesis or may be acquired as a result of lead poisoning, liver failure, or drug toxicity. The inherited porphyrias consist of eight subgroups based on which enzyme is deficient. They are divided clinically into three groups: neuropsychiatric, cutaneous, or mixed. The neurological porphyrias are not associated with anemia, but erythropoietic porphyria, a type of cutaneous porphyria, is. In general, neurological porphyrias are associated with increases in PBG and Δ-aminolevulinic acid (porphyrin precursors), whereas cutaneous porphyrias are associated with increased urinary porphyrins. No one sample type can be used to identify all subgroups, and sometimes all three are needed.

Answer 287

D Porphyria is a rare condition, although most of the inherited forms are autosomal dominant. Porphyria cutanea tarda results from a deficiency of uroporphyrinogen decarboxylase, and hence, the carboxylated forms of uroporphyrin accumulate in plasma and spill into urine. The enzyme in hepatocytes is susceptible to drugs, alcohol, and hepatitis, which trigger the disease. The disease usually appears in middle-aged adults, the majority of whom have hepatitis C infection. The uroporphyrins are highly fluorescent and may cause port wine–colored urine. Affected persons present with skin blisters and skin burns if they have been exposed to sunlight.

Answer 288

A The Watson-Schwartz test is a qualitative screening test for PBG and is based on the principle that dietary indole compounds and urobilinogen can be separated from PBG by extraction. PBG is extracted in n-butanol, whereas urobilinogen and dietary indoles are extracted into chloroform. However, the sensitivity and specificity of the test are poor in comparison with chromatographic and mass spectroscopic methods that better separate PBG from interfering substances. PBG is elevated in neurological porphyrias, the most common of which is acute intermittent porphyria.

Answer 289

D Excretion of melanin in malignant melanoma and homogentisic acid in alkaptonuria cause urine to turn black on standing. Other substances that may cause brown or black- colored urine are methemoglobin, PBG, porphobilin, and urobilin. Gantrisin, PSP dye, and rifampin are three examples of drugs that cause red or orange-red urine.

Answer 290

B Porphyria cutanea tarda and erythropoietic porphyria produce sufficient uroporphyrins to cause dark red urine. Acute intermittent porphyria produces large amounts of PBG, which may be oxidized to porphobilin, turning the urine orange to orange-brown.

Answer 291

B Standing urine may become alkaline because of loss of volatile acids and ammonia production. Bilirubin glucuronides may become hydrolyzed to unconjugated bilirubin or oxidized to biliverdin, resulting in a false-negative result on the dry reagent strip test. Glucose can be consumed by glycolysis or oxidation by cells.

Answer 292

C Urine microscopy reflex testing is used by laboratories that do not perform automated microscopic urinalysis because of the low likelihood of significant findings when the microscopic analysis is performed on samples with normal physical characteristics and biochemical results. Urine samples with abnormal color and clarity are usually included in the criteria for reflex testing because either may be associated with abnormal cells or crystals.

Answer 293

C When collecting a 24-hour urine sample, the bladder must be emptied of urine at the start of the test and discarded. The bladder must be emptied at the conclusion of the test and the urine added to the collection. To prevent degradation of the catecholamines vanillylmandelic acid (VMA), metanephrines, and cortisol, urine must be refrigerated during storage and kept at 2°C to 8°C until analysis or frozen. If the pH of the specimen exceeds 3.0, degradation of catecholamines can occur. Preservation of urine with acid is no longer required for VMA, metanephrines, and cortisol.

Answer 294

C Normal daily urine excretion is usually 600 to 1,600 mL/day. Isosthenuria refers to urine of constant SG of 1.010, which is the SG of the glomerular filtrate. Glycosuria causes retention of H2O within the tubule, resulting in dehydration and polyuria, rather than oliguria.

Answer 295

A All substances that dissolve in the urine contribute to osmotic pressure or osmolality. This includes nonionized solutes such as urea, uric acid, and glucose as well as salts, but not colloids, such as protein and lipids.

Answer 296

C In severe renal diseases, the tubules fail to concentrate the filtrate. Salt and H2O equilibrate by diffusion, causing an SG of about 1.010. If the SG of urine is below that of plasma, free H2O is lost. This results from failure to produce ADH (inherited diabetes insipidus) or from failure of the tubules to respond to ADH (nephrogenic diabetes insipidus, which can be caused by drugs, polycystic kidney disease, and hypercalcemia).

Answer 297

C Glucose and drug metabolites increase the SG of urine. In prerenal failure, the tubules are undamaged. Ineffective arterial pressure stimulates aldosterone release. This increases sodium reabsorption, which stimulates ADH release. Water and salt are retained, and the urine:plasma osmolar (U:P) ratio exceeds 2:1. Chronic renal failure is associated with nocturia, polyuria, and low SG caused by scarring of the collecting tubules.

Answer 298

C Cells and undissolved solutes refract light and will cause a falsely high specific gravity reading by refractometry if urine is not centrifuged. Colorimetric SG tests are less sensitive to nonionized compounds, such as urea and glucose, and are negatively biased when large quantities of nonelectrolytes are present. Colorimetric SG readings are determined by a pH change on the test pad and are approximately 0.005 lower when pH is 6.5 or higher. Osmometry is the most accurate way to measure the concentration of dissolved solutes in urine.

Answer 299

A A polyelectrolyte with malic acid residues will ionize in proportion to the ionic strength of urine. This causes the pH indicator, bromthymol blue, to react as if it were in a more acidic solution. The indicator will be blue at low SG and green at higher SG.

Answer 300

C Bacteriuria is usually associated with an alkaline pH caused by the production of ammonia from urea. Extended storage may result in loss of volatile acids, causing increased pH. A high-protein diet promotes excretion of inorganic acids. The tubular maximum for hydrogen ion secretion occurs when urine pH reaches 4.5, the lowest urinary pH that the kidneys can produce

Answer 301

B Renal tubular acidosis results from a defect in the renal tubular reabsorption of bicarbonate. Hydrogen ions are not secreted when bicarbonate ions are not reabsorbed. Wasting of sodium bicarbonate (NaHCO3) and potassium bicarbonate (KHCO3) results in alkaline urine and hypokalemia in association with acidosis.

Answer 302

B Under conditions of normal fluid intake, the reference range for urine volume is 0.6 to 1.6 L per day. Urine output will vary widely with fluid intake. In cases of fluid deprivation, almost all filtrate will be reabsorbed, resulting in daily excretion as low as 500 mL. When fluid intake is excessive, up to 2.0 L of urine may be voided. Urine output beyond these extremes is considered abnormal.

Answer 303

C The SG of the filtrate in the Bowman space approximates the SG of plasma because sodium, chloride, glucose, urea, and other main solutes are completely filtered by the glomeruli. This corresponds to an osmolality of approximately 280 mOsm/kg.

Answer 304

D Urine pH is determined by diet, acid–base balance, water balance, and renal function. In partially compensated respiratory alkalosis, the kidneys reabsorb less bicarbonate, which results in lower net acid excretion. The loss of bicarbonate helps compensate for alkalosis and causes urine pH to be alkaline.

Answer 305

B In addition to highly buffered alkaline urine, a false-positive protein result on the dry reagent strip test may be caused by quaternary ammonium compounds, which increase urine pH. Because the dry reagent strip tests are insensitive to globulins, a false- negative result is likely in the case of Bence-Jones proteinuria. Positive interference by drugs is uncommon for dry reagent strip protein tests but is common for turbidimetric tests. High urinary SG will suppress the color reaction of the strip protein tests.

Answer 306

B Turbidimetric assays are used to test urine suspected of giving a false-positive result on the dry reagent strip test for albumin because the urine is highly alkaline (pH greater than or equal to 8.0) or contains pigmentation that interferes with reading the protein test pad. In addition, SSA tests are used when screening urine for an increased concentration of globulins because dry reagent strip tests are far less sensitive to globulins. SSA is less specific but more sensitive for albuminuria than conventional dry reagent strip tests. Iodinated dyes, penicillin, salicylate, and tolbutamide may result in false-positive results. Trace turbidity is difficult to determine when urine is cloudy as a result of bacteriuria, mucus, or crystals. Alkaline urine may titrate SSA, reducing its sensitivity. For these reasons, the SSA test is not used routinely.

Answer 307

C The IVP dye contains iodine and is highly refractile. This increases the refractive index of urine, causing falsely high measurement of solute concentration. The refractive index is affected by the size and shape of solutes and undissolved solids, such as protein. Osmolality is the most specific measure of total solute concentration because it is affected only by the number of dissolved solutes.

Answer 308

D Dry reagent strip tests using tetrabromophenol blue or tetrachlorophenol tetrabromosulfophthalein are poorly sensitive to globulins and may not detect immunoglobulin light chains. Turbidimetric methods, such as 3% SSA, will often detect Bence-Jones protein but may give a false-positive reaction with penicillin, tolbutamide, salicylates, and x-ray contrast dyes containing iodine. Amorphous phosphates may precipitate in refrigerated urine, making interpretation of turbidimetric tests difficult.

Answer 309

D Small amounts of albumin and other low molecular weight proteins, such as amylase, β-microglobulins, and immunoglobulin fragments, are excreted in urine. Proteinuria does not normally exceed 30 mg/dL or 150 mg/day. The detection limit of the SSA test to albumin is approximately 1.5 to 2.0 mg/dL, and for dry reagent strip tests, it is approximately 15 mg/dL. Therefore, trace positives by either method may occur in the absence of renal disease

Answer 310

D Ascorbic acid may reduce diazo salts used in the bilirubin and nitrite tests, and react with hydrogen peroxide in peroxidase reactions. Therefore, persons taking megadoses of ascorbic acid (vitamin C) may show negative interference with tests for glucose, blood, bilirubin, and nitrite. Ascorbate does not cause either a false-negative or positive reaction for protein.

Answer 311

A The microalbumin test is an assay for measuring urinary albumin concentration that has an increased sensitivity (detection limit below 15 mg/dL) and is recommended for persons who are at risk for chronic renal disease, especially persons with diabetes mellitus. In diabetes, an early sign of renal involvement is an increased rate of albumin excretion in the range of 20 to 200 μg/mL or in excess of 30 mg albumin per gram of creatinine. Results in this range are significant in the at-risk population, even though the dry reagent strip test for protein may yield negative results. Dry reagent strip tests for microalbuminuria are too sensitive for use in routine urinalysis but are useful in screening persons with diabetes and hypertension for increased urinary albumin excretion

Answer 312

A The dry reagent strip test for creatinine contains anhydrous buffered copper II sulfate (CuIISO4), alcoholic tetramethylbenzidine, and diisopropyl benzene dihydroperoxide. In the presence of creatinine, a copper–creatinine complex forms. This catalyzes the oxidation of a benzidine derivative by an alcoholic peroxide, forming a blue color on the test pad. Color intensity is proportional to creatinine concentration. Negative interference occurs from ascorbate and ethylenediaminetetraacetic acid (EDTA), which chelates the copper. Positive interference occurs from hemoglobin and some drugs (e.g., nitrofurantoin). The microalbumin concentration is determined by the protein error of indicator effect using a dye with increased sensitivity, bis- tetrabromosulfonephthalein.

Answer 313

D The detection limit (sensitivity) of dry reagent strip protein tests is approximately 15 mg/dL albumin and is sufficient to detect urinary albumin levels found in orthostatic albuminuria and renal diseases, with the exception of tubular proteinuria. Renal tubular proteinuria results from failure of damaged tubules to reabsorb small proteins, such as β2-microglobulin. Dry reagent strip tests for proteinuria are poorly sensitive to globulins and do not detect small quantities of hemoglobin, myoglobin, or microglobulins. Electrophoresis of urine is used to detect renal tubular proteinuria

Answer 314

D The renal threshold is the concentration of a substance (e.g., glucose) in blood that must be exceeded before it can be detected in urine. Threshold substances require a carrier to transport them from the tubular lumen to the vasa recta. When the carrier becomes saturated, the tubular maximum is reached, causing the substance to be excreted in urine.

Answer 315

C In addition to diabetes mellitus, glycosuria may occur in other endocrine diseases, in pregnancy, in response to drugs that affect glucose tolerance or renal threshold, and in several other conditions, especially those involving the liver or the central nervous system (CNS). Cushing disease and hyperthyroidism cause impaired glucose tolerance and hyperglycemia. Increased estrogens produced in pregnancy lower the renal threshold for glucose and may impair glucose tolerance. Hyperpituitarism causes hyperglycemia mediated by increased release of growth hormone.

Answer 316

A AAA and salicylates may inhibit the glucose oxidase reaction by the same mechanism as ascorbate. These reducing agents compete with the chromogen for hydrogen peroxide. Low SG may increase and high SG decrease the color reaction for glucose in urine.

Answer 317

A Glucose oxidase is specific for β-D-glucose. Therefore, a positive reaction is always considered significant unless contamination is evident. A reducing test should not be used to confirm a positive result on the glucose oxidase test because this test is not as specific or as sensitive. Reducing sugar tests are used to screen infants for inborn errors of carbohydrate metabolism, such as galactosuria, but are not used to screen for glycosuria.

Answer 318

C Reducing tests utilize alkaline copper sulfate and heat to oxidize glucose. Other reducing substances, including several sugars and antibiotics, may react, making the test inappropriate as a screening test for glucose. A positive test result for reducing sugars seen with a negative glucose oxidase test result may occur in lactose, galactose, and fructosuria and other disorders of carbohydrate metabolism. Such tests should always be confirmed with chromatography to identify the specific sugar and with assay of the specific enzyme involved

Answer 319

A Tests for urinary ketone bodies are sensitive to AAA. They react weakly with acetone and do not react with β-hydroxybutyric acid. Acidosis favors formation of β- hydroxybutyric acid and may cause a falsely low estimate of urine ketones in diabetic ketoacidosis. Ketonuria has many causes other than diabetic ketoacidosis, such as pregnancy, fever, protein calorie malnutrition, and dietary carbohydrate restriction. Trace ketones tend to be more clinically significant when seen in urine with a low SG.

Answer 320

A Urinary ketones are detected using alkaline sodium nitroprusside (nitroferricyanide). Mesna and other sulfhydryl compounds may cause a false-positive result on dry reagent strip tests and phenylpyruvic acid (PKU) and some antibiotics with the classic tube test.

Answer 321

B Ketonuria results from excessive oxidation of fats forming acetyl coenzyme A (CoA). In addition to diabetes mellitus, ketonuria occurs in starvation, carbohydrate restriction, alkalosis, lactate acidosis, and von Gierke disease (glycogen stores cannot be utilized). Ketonuria also occurs in pregnancy, associated with increased vomiting and cyclic fever.

Answer 322

C Tests for ketones are less sensitive to acetone than to AAA and do not detect β- hydroxybutyric acid. High levels of phenylpyruvic acid (phenylketonuria) will cause a false-positive reaction in the classic nitroprusside reaction but do not usually interfere with the dry reagent strip test for ketones. Serum ketones can be measured by gas chromatography, and β-hydroxybutyric acid can be measured enzymatically. The enzymatic assay for β-hydroxybutyrate in plasma is the recommended test for diagnosing ketoacidosis since acidosis favors its formation

Answer 323

A Both hemoglobin and myoglobin have peroxidase activity and cause a positive blood test result. However, myoglobin is soluble in 80% weight per volume (w/v) ammonium sulfate in urine, but hemoglobin precipitates. A positive blood reaction with supernatant after addition of ammonium sulfate and sodium hydroxide (NaOH) confirms the presence of myoglobin. The presence of RBCs indicates that hemoglobin, rather than myoglobin, is present; however, the absence of RBCs does not rule out the presence of hemoglobin as the cause of a positive blood test result.

Answer 324

D A positive result on the blood test can occur from renal or lower urinary tract bleeding, intravascular hemolytic anemia, and transfusion reaction. Extravascular hemolysis results in increased bilirubin production, rather than in plasma hemoglobin. This may cause increased urobilinogen in urine, but not a positive blood reaction.

Answer 325

B The blood reaction uses anhydrous peroxide and tetramethylbenzidine. Hemoglobin has peroxidase activity and catalyzes the oxidation of tetramethylbenzidine by peroxide. The reaction is sensitive to submilligram levels of free hemoglobin, whereas visible hemolysis does not occur unless free hemoglobin exceeds 20 mg/dL. The test detects approximately 4–5 intact RBCs/HPF as a nonhemolyzed trace. Greater than 3 RBCs/HPF is abnormal

Answer 326

D The blood test detects intact RBCs, hemoglobinuria, and myoglobinuria. Causes of hemoglobinuria include intravascular hemolytic anemias, transfusion reactions, and lysis of RBCs in the filtrate or urine caused by alkaline or hypotonic conditions. Causes of hematuria include acute and chronic glomerulonephritis, pyelonephritis, polycystic kidney disease, renal calculi, bladder and renal cancers, and catheterization of the urinary tract.

Answer 327

C The blood test detects as little as 0.015 mg/dL free hemoglobin and 4 to 5 RBCs/μL. The protein test detects 15 mg/dL albumin, but substantially more hemoglobin is required to obtain a positive test result. Therefore, a small blood reaction (nonhemolyzed or moderately hemolyzed trace, trace, or small) usually occurs in the absence of a positive protein. A positive blood test result often occurs in the absence of RBCs in the microscopic examination. This can result from intravascular hemolysis, myoglobinuria, or lysis of RBCs caused by alkaline or hypotonic urine. A positive test result for protein and a negative blood test result occur commonly in such conditions as orthostatic albuminuria, urinary tract infection, and diabetes mellitus. However, a negative blood test result should not occur if more than 3 to 4 RBCs/HPF are seen in the microscopic examination. Either the blood test is falsely negative (a missed nonhemolyzed trace), or yeast has been mistaken for RBCs.

Answer 328

B Only the conjugated form of bilirubin is excreted into urine. Urinary bilirubin is positive in necrotic and obstructive jaundice but not in prehepatic jaundice, which results in a high level of serum unconjugated bilirubin. The highest levels of urinary bilirubin occur in obstructive jaundice, which causes decreased urinary urobilinogen. Very few drugs have been reported to interfere with urine bilirubin tests, which are based on the formation of azobilirubin by reaction with a diazonium salt. Positive interference by rifampin and chlorpromazine have been reported. Urine must be fresh because sunlight destroys bilirubin. Bacteria may cause hydrolysis of glucuronides, forming unconjugated bilirubin, which does not react with the diazonium reagent. Ascorbate inhibits the reaction by reducing the diazo reagent.

Answer 329

C Urobilinogen reacts with the Ehrlich aldehyde reagent (p- dimethylaminobenzaldehyde in hydrochloric acid [HCl]) to form a pink color. Dry reagent strips use either p-dimethylaminobenzaldehyde or 4-methoxybenzene diazonium tetrafluoroborate to detect urobilinogen. The former reagent may react with PBG, salicylate, and sulfonamides giving falsely high results. False-positive results may occur in the presence of pyridium and gantrisin, which color urine orange-red. Formalin may cause a false-negative reaction

Answer 330

C Urobilinogen exhibits diurnal variation, and highest levels are seen in the afternoon. A 2-hour postprandial afternoon sample is the sample of choice for detecting increased urine urobilinogen. Urobilinogen is formed by bacterial reduction of conjugated bilirubin in the bowel. In obstructive jaundice, delivery of bilirubin into the intestine is blocked, resulting in decreased fecal, serum, and urine urobilinogen. However, the dry reagent strip tests are not sensitive enough to detect abnormally low levels. Urobilinogen is rapidly oxidized to urobilin, which does not react with dry reagent strip tests.

Answer 331

C The nitrite test is dependent on the activity of bacterial reductase, and false-negative results have been reported when urine is highly acidic. Nitrite is formed by reduction of diet-derived nitrates and reacts with p-arsanilic acid or sulfanilamide to form a diazonium compound. This reacts with benzoquinoline to form a pink azo dye. False- negative results also occur in the presence of ascorbate, which reduces the diazonium product. Nitrite is positive in about 70% of clinically significant bacterial infections of the urinary tract. Sensitivity is limited by the requirements for dietary nitrate and 3- to 4-hour storage time in the bladder. In addition, the causative bacteria must be able to reduce nitrate.

Answer 332

B Polymorphonuclear cells (PMNs) in urine are detected by the presence of esterases that hydrolyze an ester, such as indoxylcarbonic acid. The product reacts with a diazonium salt to give a purple color. The test detects esterases in urine as well as intact WBCs but is not sensitive to less than 5 to 10 WBCs/HPF. Several antibiotics, high protein, and high SG inhibit the esterase reaction. Formalin may cause a false- positive result.

Answer 333

D Although some creatinine is derived from the diet, it is rapidly filtered by the glomeruli, and time variations are reduced by collection of urine for 24 hours. Creatinine is produced from oxidation of creatine at a constant rate of about 2% per day. It is filtered completely and not significantly reabsorbed. However, creatinine secretion by the tubules is increased when filtrate flow is slow, and patients must be given at least 600 mL of H2O at the start of the test and kept well hydrated throughout. Body size determines how much creatinine is produced, and clearance must be normalized to eliminate this variable. Because of the difficulty in collecting a valid 24- hour urine sample, the estimated glomerular filtration rate (eGFR) is recommended as the screening test for low GFR. Creatinine clearance should be used in situations where lean body mass may not be accurately represented by the patient’s age and gender as used in the Modification of Diet in Renal Disease Study (MDRD) formula for eGFR.

Answer 334

D Normal eGFR is 90 to 120 mL/min. Values below the lower reference limit, but greater than 60 mL/min, indicate glomerular damage but not of severity sufficient to cause symptoms or uremia

Answer 335

D Cystatin C is a small protease inhibitor that is produced at a constant rate, eliminated exclusively by glomerular filtration, and is not dependent on age, gender, or nutritional status. Plasma cystatin C is increased when the GFR is decreased, and levels can be used to give an eGFR in a similar manner to plasma creatinine. PAH is a substance that is completely filtered by the glomerulus and also secreted by the tubules. Amino acids are partially reabsorbed by the tubules and are not present in blood at a constant rate

Answer 336

A Blood urea nitrogen (BUN) is a sensitive indicator of renal disease but is not specific for glomerular function. BUN levels are affected by diet, hepatic function, tubular function, and filtrate flow, as well as the GFR. Although urea is completely filtered by the glomerulus, the tubules reabsorb 30% to 40% of the filtered urea, and this is why BUN concentration is higher than plasma creatinine. In prerenal failure, up to 70% of the filtered urea can be reabsorbed as a result of the slow movement of filtrate through the tubules. This causes BUN to rise much more than plasma creatinine in this condition. A BUN:creatinine ratio of 20:1 is highly suggestive of prerenal failure

Answer 337

B The clearance formula is U ÷ P × V × 1.73/A, where U = urine creatinine (mg/dL), P = plasma creatinine (mg/dL), V = urine volume (mL/min), and 1.73 = mean body surface area (m2): 100 mg/dL ÷ 1.2 mg/dL × 1.4L/day × 1,000 mL/L × 1 day/1,440 min × (1.73 m2 ÷ 1.8 m2) = 78 mL/min Note that the creatinine clearance is low (lower reference limit approximately 95 mL/min for males and 85 mL/min for females), although the serum creatinine is still within normal limits (0.5–1.2 mg/dL). The clearance test is more sensitive if done properly because as serum creatinine goes up, urine creatinine goes down.

Answer 338

B The Sternheimer-Malbin stain is a supravital stain used to differentiate renal tubular epithelium from transitional cells and PMNs. The mononuclear cells are clearly distinguished from both live and dead PMNs. Transitional cells have pale blue cytoplasm, but renal cells take up both dyes, resulting in an azurophilic appearance (orange-purple cytoplasm and dark purple nucleus).

Answer 339

D The majority of WBCs in urinary sediment will be PMNs. Eosinophils and mononuclear WBCs will occasionally be seen. High numbers of eosinophils often indicate an allergic drug reaction, causing inflammation in the medullary interstitium and tubules. Mononuclear cells are especially likely in patients with chronic inflammatory diseases and in renal transplant rejection, where they may account for as many as 30% of the WBCs. Glitter cells are PMNs with highly refractile granules exhibiting Brownian movement. They are seen only when the urine SG is below 1.020. These cells resist staining with the Sternheimer-Malbin stain and are considered to be living (fresh) WBCs. When seen in large numbers, they indicate urinary tract injury (with pseudopod extensions, they point to infection). The presence of bacteria in urine in the absence of PMNs usually results from contamination by vaginal or skin flora that multiply in vitro, especially in unrefrigerated specimens. The presence of WBC casts is always significant and, when associated with pyuria and bacteriuria, indicates renal involvement in the infection

Answer 340

A After staining with the Sternheimer-Malbin stain, transitional epithelium are readily differentiated from renal tubular cells and WBCs because their cytoplasm is pale blue. Live WBCs exclude the Sternheimer-Malbin stain, whereas dead cells stain with a deeply blue-purple nucleus and pale orange-blue cytoplasm. Renal epithelium have an orange-purple cytoplasm and dark purple nucleus. Squamous epithelium have a blue or purple cytoplasm and an orange-purple nucleus. Red cells stain very pale pink or not at all and hyaline casts stain faintly pink.

Answer 341

C Given the SG and pH, most RBCs and WBCs will be intact. Both the RBC and WBC counts are lower than expected from the dry reagent strip test results. Myoglobin or free hemoglobin may account for the poor correlation between the blood reaction and the RBC count, but this does not explain the lower than expected WBC count. Microscopic reference ranges are based on concentrating a uniform volume of sediment from 12 mL of urine. When less urine is used, falsely low results will be obtained unless corrective action is taken. The specimen should be diluted with normal saline to 12 mL, then centrifuged at 450 × g for 5 minutes. Urinary sediment should be prepared according to the established procedure and the results multiplied by the dilution factor (in this case, 12 ÷ 5, or 2.4).

Answer 342

B Caudate cells are transitional epithelium that have a sawtooth-shaped tail and are found in the urinary bladder and the pelvis of the kidney. Transitional epithelia line the upper two thirds of the urethra and the ureters as well as the urinary bladder and renal pelvis. Renal tubular cells may be columnar, polyhedral, or oval, depending on the portion of the tubule from which they originate. Cells from the proximal tubule are columnar and have a distinctive brush border. Squamous epithelia line the vagina and lower third of the urethra.

Answer 343

B Renal cells and PMNs are about the same size and can be confused in unstained sediment. Catheterization often releases large clumps or sheets of transitional and squamous cells. These should be distinguished from neoplastic cells derived from the urinary bladder. When cells appear atypical (e.g., large cells in metaphase), they should be referred to a pathologist for cytological examination. Nonbudding yeast cells are approximately the same in size and appearance as RBCs. When RBCs are reported in the absence of a positive blood test, the probability of an error in microscopy is high. The microscopic examination should be reviewed for the presence of yeast

Answer 344

B Transitional epithelial cells readily take up H2O and appear much larger than renal cells or WBCs when urine is hypotonic. Transitional cells are considered a normal component of the sediment unless present in large numbers and associated with signs of inflammation, such as mucus and PMNs, or presenting features of malignant cells. In contrast, renal cells are significant when seen conclusively in the sediment. They are often teardrop-shaped, polyhedral, or elongated cells with a round eccentric nucleus. Conclusive identification requires staining. T. vaginalis displays an indistinct nucleus and two pairs of prominent anterior flagella. Amorphous urate crystals deposited on the slide may be mistaken for granular or blood casts.

Answer 345

C RBCs are difficult to distinguish from nonbudding yeast in unstained sediment. RBCs tumble when the cover glass is touched and will lyse when the sediment is reconstituted in normal saline containing 2% volume per volume (v/v) acetic acid. A nonhemolyzed trace blood reaction confirms the presence of RBCs. RBCs have a granular appearance in hypertonic urine as a result of crenation. The RBC membrane becomes distorted when passing through the glomerulus, often appearing scalloped, serrated, or invaginated. Such cells are called dysmorphic RBCs and are associated with glomerulonephritis.

Answer 346

D Although seen in glomerulonephritis and pyelonephritis, the largest numbers of renal tubular cells appear in urine in association with viral infections of the kidney. Renal epithelium may show characteristic viral inclusions associated with CMV and rubella. High numbers of renal epithelium are also found in the sediment of patients with drug- induced tubular nephrosis and in some cases of heavy metal poisoning. Renal tumors do not usually shed cells into urine

Answer 347

C Ova of S. hematobium are most often recovered from urine because the adult trematodes colonize the blood vessels of the urinary bladder. The eggs are approximately 150 × 60 μm in size and are nonoperculated. They are yellowish and have a prominent terminal spine.

Answer 348

B Oval fat bodies are degenerated renal tubular epithelia that have reabsorbed cholesterol from the filtrate. Although they can occur in any inflammatory disease of the tubules, they are commonly seen in nephrotic syndrome, which is characterized by marked proteinuria and hyperlipidemia.

Answer 349

A Proteinuria accompanies cylindruria because protein is the principal component of casts. After strenuous exercise, hyaline casts may be present in urinary sediment in significant numbers but will disappear after resting for at least 24 hours. Casts more readily dissolve in alkaline urine. The finding of a single cast, even a cellular cast, is not indicative of renal disease and should be considered a chance occurrence.

Answer 350

C Cast formation is promoted by an acid filtrate, high solute concentration, slow movement of filtrate, and reduced filtrate formation. The appearance of a cast is dependent on the location and the time spent in the tubule, as well as the chemical and cellular composition of the filtrate.

Answer 351

C Hyaline casts are composed of a mucoprotein called Tamm-Horsfall protein. In addition, casts may contain cells, immunoglobulins, light chains, cellular proteins, fat, bacteria, and crystalloids.

Answer 352

C Pseudocasts are formed by amorphous urates that may deposit in uniform cylindrical shapes as the sediment settles under the cover glass. They may be mistaken for granular or blood casts. However, they are highly refractile and lack the well-defined borders of true casts.

Answer 353

D There is no clinical difference between fine and coarse granular casts. Granular casts may form by degeneration of cellular casts or from inclusion of urinary calculi, but some are of unknown etiology. Cylindruria refers to the presence of casts in the urine. Hyaline casts may be seen in small numbers in normal patients and in large numbers following strenuous exercise and long-distance running. Hyaline casts may also be increased in patients taking certain drugs, such as diuretics. Broad casts form in dilated or distal tubules and indicate severe tubular obstruction seen in chronic renal failure. Waxy casts form when there is prolonged stasis in the tubules and signal end-stage renal failure. Cylindroids are casts with tails and have no special clinical significance

Answer 354

C RBC casts indicate the renal origin of hematuria. Urinary tract obstruction may be associated with hematuria from ruptured vessels, but not casts. WBCs and WBC casts predominate in pyelonephritis. Urinary sediment in chronic glomerulonephritis is variable but usually exhibits moderate to severe intermittent hematuria. In addition, pyuria and cylindruria (with granular, blood, broad, waxy, and epithelial casts) are frequent. In nephrotic syndrome, the sediment may be unremarkable except for the presence of oval fat bodies and hyaline casts. In some cases, fatty, waxy, and epithelial cell casts may also be found.

Answer 355

B Pyelonephritis results from bacterial infection of the renal pelvis and interstitium. It is characterized by polyuria resulting from failure of the tubules to reabsorb fluid. Compression and obstruction of the tubules by WBCs reduces H2O reabsorption. The finding of WBC casts helps differentiate pyelonephritis from UTI

Answer 356

C Waxy casts form from the degeneration of cellular casts. Because the casts must remain lodged in the tubule long enough for the granular protein matrix to waxify, they are associated with chronic and end-stage renal failure. Both waxy and broad casts form in chronic renal failure when there is severe stasis, and they are associated with a poor prognosis.

Answer 357

D A positive blood test result and trace protein occurring with a normal test for urobilinogen and an absence of RBCs are consistent with an intravascular transfusion reaction. Small, yellow-brown granular crystals at an acid pH may be uric acid, bilirubin, or hemosiderin. Bilirubin crystals are ruled out by the negative result on the dry reagent strip test for bilirubin. Potassium ferrocyanide is used in the Prussian blue staining reaction to detect hemosiderin deposits in urinary sediment. Hemosiderin is associated with hemochromatosis and increased RBC destruction. Causes of urinary hemosiderin include transfusion reaction, intravascular hemolytic anemia, and pernicious anemia.

Answer 358

C Epithelial casts are rarely seen but indicate a disease process affecting the renal tubules. They are associated with diseases causing necrosis of the tubules, such as hepatitis, CMV and other viral infections, and mercury and ethylene glycol toxicity. Even occasional cellular casts are considered clinically significant.

Answer 359

B Urates are yellow-brown or reddish-brown granules and form in acid or neutral urine. They often form following refrigeration of urine and can be dissolved by addition of warm saline or dilute NaOH. Amorphous phosphates are colorless and form in neutral or alkaline urine. They dissolve in dilute acetic acid but precipitate if heated.

Answer 360

B Flat, six-sided uric acid crystals may be mistaken for cystine crystals. Both crystals form at an acid to neutral pH. Cystine crystals are colorless, whereas uric acid crystals are pigmented (yellow, reddish brown). Cystine transmits polarized light and is soluble in dilute HCl. Uric acid is insoluble in HCl and is less anisotropic. Cystine is reduced by sodium cyanide, forming cysteine. The -SH group of cysteine reacts with nitroprusside to form a red color.

Answer 361

B Tyrosine crystals may occur in tyrosinemia, an inborn error of tyrosine metabolism caused by a deficiency of fumarylacetoacetate hydrolase, p-hydroxyphenylpyruvic acid oxidase, or tyrosine aminotransferase (causes of tyrosinuria). However, when seen along with leucine crystals, the cause is chronic liver disease, usually cirrhosis of the liver. Tyrosine usually forms fine brown or yellow needles, and leucine forms yellow spheres with concentric rings.

Answer 362

C Abnormal crystals are those that result from a pathological process. Hemosiderin crystals result from intravascular RBC destruction. Bilirubin crystals are found in severe necrotic and obstructive liver diseases, and cholesterol crystals in nephrotic syndrome, diabetes mellitus, and hypercholesterolemia

Answer 363

D Ammonium biurate is often called a “thornapple” crystal because it forms a dark brown spiny sphere. Calcium carbonate (CaCO3) is another common crystal that is seen only in alkaline urine. Sodium urate and uric acid form in acid or neutral urine

Answer 364

C Magnesium ammonium phosphate, also called triple phosphate, may be present in neutral or alkaline urine. Most commonly, triple phosphate crystals are six-sided plates that resemble a coffin lid. Crystals containing phosphates do not occur in acid urine

Answer 365

B Hippuric acid forms long, colorless, flat, six-sided plates. It results from the metabolism of benzoic acid and resembles the “coffin lid” appearance of triple phosphate. It may occur normally as a result of ingestion of vegetables preserved with benzoic acid.

Answer 366

D Cholesterol crystals are colorless rectangular plates that often have a notched corner and appear stacked in a stair-step arrangement. Cholesterol crystals are highly anisotropic and can be positively identified by using a polarizing microscope. Bilirubin, sulfa, or uric acid crystals may occur as small yellow or yellow-brown needles or rods in neutral or acid urine. Bilirubin crystals should be suspected when the dry reagent strip test for bilirubin yields a positive result and cells in the sediment are dark yellow (bile stained). Sulfa crystals are soluble in acetone, concentrated HCl, and NaOH.

Answer 367

A Oval fat bodies form from degenerated renal epithelial cells that have reabsorbed cholesterol from the filtrate. They stain with Oil Red O or Sudan III. The fat globules within the cells give a Maltese cross effect when examined under polarized light.

Answer 368

A The term lipoid nephrosis is a synonym for idiopathic (primary) nephrotic syndrome. Like other forms of nephrotic syndrome, it is associated with gross proteinuria, edema, and hyperlipidemia; however, the idiopathic form is also associated with hematuria. It is common in children and is often associated with mutations that affect podocyte structure

Answer 369

B The SG of the filtrate in the Bowman space is approximately 1.010. Urine produced consistently with a SG of 1.010 has the same osmolality of the plasma and results from failure of the tubules to modify the filtrate.

Answer 370

A Prerenal failure is caused by deficient renal blood flow. The tubules are undamaged and will reabsorb more BUN than normal because filtrate flow is slow. Under the influence of aldosterone, they reabsorb sodium and concentrate the urine. The BUN:creatinine ratio and the U:P osmolal ratio are very high, and sodium output is low. In renal disease, the BUN:creatinine ratio is 10 or less, the U:P osmolal ratio approaches 1.0, and the daily sodium excretion is high.

Answer 371

B Acute glomerulonephritis results in severe compression of the glomerular vessels. This reduces filtration, causing a progression from oliguria to anuria. In contrast, polyuria is associated with chronic glomerulonephritis, which causes scarring of the collecting tubules. Both acute and chronic glomerulonephritis cause low urine osmolality, azotemia, acidosis, hypertension, proteinuria, and hematuria.

Answer 372

D Reduced glomerular filtration as evidenced by low creatinine clearance characterizes both prerenal failure and acute renal failure. This results in retention of fluid, causing edema, reduced urine volume, hypertension, uremia, and hyperkalemia in both prerenal failure and acute renal failure. The kidneys are not damaged in prerenal failure, and therefore, the microscopic examination is usually normal

Answer 373

A In acute renal failure, reduced glomerular filtration coupled with decreased tubular secretion results in hyperkalemia. In chronic renal failure, scarring of the collecting tubules prevents salt and H2O reabsorption. This can result in normal or low serum potassium despite reduced glomerular filtration. The sediment in chronic renal failure is characterized by intermittent heavy hematuria and proteinuria.

Answer 374

C Decreased glomerular filtration in renal failure results in high serum creatinine, BUN, and uric acid. Failure of the tubules results in retention of hydrogen ions and phosphates, causing acidosis and an increased anion gap. The tubules fail to respond to parathyroid hormone, resulting in excessive loss of calcium in urine. Serum sodium is usually normal or slightly increased, whereas hyperkalemia is a constant finding in acute renal failure.

Answer 375

C Although all four conditions are associated with proteinuria, it is greatest in nephrotic syndrome. Urinary albumin loss is typically in excess of 4 g/day or 3 mg/mg creatinine, causing dry reagent strip protein tests to give 3+ to 4+ reactions. In contrast to glomerulonephritis and pyelonephritis, urinary sediment in nephrotic syndrome in adults is not usually characterized by either hematuria or pyuria. Various casts, lipid laden renal epithelial cells, and oval fat bodies are usually found.

Answer 376

C Autoimmune diseases, diabetes mellitus, and nephrotoxic drugs are common causes of acute glomerulonephritis. Autoimmune damage may result from the deposition of antigen–antibody complexes and complement-mediated damage, as occurs in poststreptococcal glomerulonephritis, or from the production of autoantibodies that attack the basement membrane as in Goodpasture syndrome. Acute glomerulonephritis is often classified by the pattern of injury rather than by the cause. For example, insulin deficiency produces sclerotic vascular damage to the glomeruli, often resulting in crescentic glomerulonephritis. Group A Streptococcus and SLE result in immunologically mediated damage to the glomeruli usually causing membranous or membranoproliferative glomerulonephritis. CMV infections and heavy metal poisoning cause damage to the tubules, resulting in nephrosis.

Answer 377

A Acute pyelonephritis is caused by infection of the medullary interstitium, usually by coliforms that enter from the lower urinary tract. Escherichia coli is the most commonly implicated bacterium. Because it is focused in the medulla, the disease involves mainly the tubules. As opposed to acute glomerulonephritis, pyelonephritis is not associated with reduced creatinine clearance, azotemia, or oliguria. Reabsorption of salt and water are blocked, resulting in hyperkalemia, acidosis, and polyuria.

Answer 378

A Although casts may be present, the urinary sediment in nephrotic syndrome in adults is not characterized by RBCs and WBCs or by RBC, blood, and WBC casts. In nephrotic syndrome, unlike renal failure (nephritic syndrome), the creatinine clearance and serum potassium are usually normal. Nephrotic syndrome can be secondary to other renal diseases, infections, and drug treatment. In such cases, it is often transient. When it follows the anuric phase of acute glomerulonephritis, it signals a reversal in the course of the disease.

Answer 379

B Obstructive renal disease may result from renal or urinary tract calculi, benign prostatic hypertrophy, chronic urinary tract infection, or urogenital malignancy. Obstruction causes the hydrostatic pressure in the Bowman space to increase. This pressure opposes glomerular filtration. If the hydrostatic pressure in the Bowman space equals the hydrostatic pressure in the glomeruli, then filtration will not occur, resulting in anuria. Postrenal failure produces many of the same serum abnormalities as acute renal failure, including hyperkalemia, acidosis, edema, and azotemia. Urinary sediment will often be abnormal, as well. Bacteriuria and pyuria are common, and hematuria may result from rupture of the vasa recta or other blood vessels.

Answer 380

B Over three-fourths of urinary tract stones are composed of calcium salts, and hyperparathyroidism is commonly associated with calcium stones. Stones composed of magnesium ammonium phosphate are called struvite and lodge in the renal pelvis, causing a characteristic “staghorn” appearance on radiographic examination. Stones mainly composed of calcium phosphate are called hydroxyapatite or bushite, depending on the calcium composition. Stones of CaCO3 are called carbonate apatite.

Answer 381

A Cystinuria is caused by an autosomal recessive defect in the tubular reabsorption of dibasic amino acids (a renal-type aminoaciduria). Cystine crystals are highly insoluble and form kidney stones. Tyrosine crystals form fine dark sheaves or needles and may result from liver disease or tyrosinosis, an overflow aminoaciduria. Leucine crystals form yellow spheres with concentric rings and are seen in chronic liver disease. Ampicillin (rarely) forms long colorless prisms in sheaves in some patients being treated with high doses

Answer 382

A Three-fourths of all stones contain calcium, and three-fourths of these contain calcium oxalate. Stones are usually composed of several inorganic salts, but calcium oxalate is the most common component of urinary stones. Oxalates are hard, dark, and coarse stones. Uric acid stones are always pigmented yellow to reddish brown. They are small translucent stones not apparent on radiography. Stones made of primarily calcium phosphate (as hydroxyapatite) are light and crumble easily. Stones made of struvite (ammonium magnesium phosphate) are radiodense and lodge in the renal pelvis, forming an outline of the structures resembling the antlers of a deer (staghorn calculi).

Answer 383

A CSF is formed by ultrafiltration of plasma through the choroid plexus, a tuft of capillaries in the pia mater located in the third and fourth ventricles. Endothelia of the choroid plexus vessels and ependymal cells lining the ventricles act as a barrier to the passage of proteins, drugs, and metabolites. Glucose in CSF is about 60% of the plasma glucose. Total protein in CSF is only 15 to 45 mg/dL, while chloride levels are 10% to 15% higher than plasma. Approximately 500 mL of ultrafiltrate is produced per day, the bulk of which is returned to the circulation via the sagittal sinus. The normal volume of CSF in adults is 100 to 160 mL (10–60 mL for small children).

Answer 384

A Normal CSF volume in adults is 100 to 160 mL. When volume is low, an abnormally high difference is observed between the opening and closing pressure. The difference is normally 10 to 30 mm H20, after removal of 15 to 20 mL. Low opening pressure is caused by reduced volume or block above the puncture site. High opening pressure may result from high CSF volume, CNS hemorrhage, or malignancy.

Answer 385

A Lymphocytes account for 40% to 80% of WBCs in adults; monocytes and macrophages for 20% to 50%. Neutrophils should be less than 10% of the WBCs. The reference range for WBCs in adults is 0 to 5/μL. A majority of PMNs can be significant even if the WBC count is normal. In infants, monocytes account for 50% to 90% of WBCs, and the upper limit for WBCs is 30/μL. The first aliquot is sent to the chemistry department because it may be contaminated with blood or skin flora.

Answer 386

C Xanthochromia is pigmentation of CSF caused by subarachnoid hemorrhage, high CSF protein, free hemoglobin, or bilirubin. The bilirubin may be caused by hepatic disease, CNS hemorrhage, or prior traumatic tap. In subarachnoid hemorrhage, the fluid will be pink if the RBC count is greater than 500/μL It will turn orange as RBCs lyse in the first few hours and then will turn yellow after about 12 hours. Granulocyte infiltration occurs immediately after a subarachnoid hemorrhage and disappears after 24 hours. It is followed by an increase in macrophages, showing evidence of erythrophagocytosis that remains for up to 2 weeks. After subarachnoid hemorrhage, D-dimer is present in CSF and can be used to distinguish between a traumatic tap and subarachnoid hemorrhage.

Answer 387

C Pleocytosis refers to an increase in WBCs within CSF. Bacterial meningitis causes a neutrophilic pleocytosis, viral meningitis a lymphocytic pleocytosis, and tuberculous and fungal meningitis a mixed-cell pleocytosis. Other causes of pleocytosis include multiple sclerosis (MS), cerebral hemorrhage or infarction, and leukemia

Answer 388

C Normal WBC counts for CSF are 0 to 5/μL for adults and 0 to 30/μL for children. Neutrophils predominate the differential in bacterial meningitis, whereas lymphocytes predominate in viral meningitis. Hemorrhage and traumatic tap will also cause increased PMNs, and WBC counts should be corrected using the CSF RBC count.

Answer 389

B Corrected WBC count = WBCs in CSF – [(Blood WBCs × CSF RBCs) ÷ Blood RBCs] Corrected WBC count = 150/μL – [(5,000/μL WBCs × 6,000/μL RBCs) ÷ 4,000,000/μL RBCs] Corrected WBC count = 150/μL – 7.5/μL Corrected WBC count = 142/μL

Answer 390

D Acute bacterial meningitis causes increased production of immunoglobulin (Ig) in CSF. Glucose levels are below normal (less than 40 mg/dL) as a result of consumption by PMNs and bacteria. Lactate levels rise because of increased pressure and hypoxia (greater than 35 mg/dL being correlated with bacterial meningitis). When associated with increased PMNs and lactate dehydrogenase (LD), these findings point to bacterial meningitis.

Answer 391

D In viral (aseptic) meningitis, the CSF glucose is usually above 40 mg/dL and the total protein is normal or slightly increased. Some types of viral meningitis can cause low glucose and high protein levels, making the differentiation of bacterial and viral meningitis difficult. In such cases, an elevated CSF C-reactive protein (CRP) and procalcitonin (PCT) strongly support the diagnosis of bacterial meningitis. PCT is increased in response to inflammation. Like lactate and CRP, it is useful for diagnosis of septic shock and following the response to antibiotic therapy. Low CSF glucose and elevated total protein are also seen in malignancy and subarachnoid hemorrhage and in some persons with MS. Low glucose in malignancy and MS results from increased utilization. Glucose is reduced in subarachnoid hemorrhage as a result of release of glycolytic enzymes from the RBCs. All three conditions result in high CSF protein, but MS is associated with an increased IgG index owing to local production of IgG.

Answer 392

C The total CSF protein is increased in less than half of persons with MS. The IgG index is increased in 80% or more of MS cases. Although the IgG index is sensitive, it is increased in many other disorders. The presence of oligoclonal banding (two or more discrete bands in the gamma zone following electrophoresis) is seen in 90% of persons with MS, and in few other diseases. Although not entirely definitive, it is the single most effective laboratory test for the diagnosis of MS. When performing CSF electrophoresis, the serum pattern must be compared with the CSF pattern. At least some of the oligoclonal bands must not be found in the serum pattern for the test result to be considered positive. β2-Microglobulins are increased in CSF in inflammatory diseases (especially malignant diseases)

Answer 393

B In fungal meningitis, the glucose is low and the total protein elevated; however, unlike bacterial meningitis, the lactate is usually below 35 mg/dL. Fungal meningitis usually produces a pleocytosis of mixed cellularity consisting of lymphocytes, PMNs, monocytes, and eosinophils. In some cases, lymphocytes predominate, whereas in others, PMNs comprise the majority of WBCs.

Answer 394

B Amoeba in CSF appear very similar to monocytes in stained films but can be differentiated by their characteristic pseudopod mobility in a wet prep on a prewarmed slide. Naegleria fowleri and Acanthamoeba spp. are causative agents of primary amoebic meningoencephalitis

Answer 395

C IgG Index = (CSF IgG divided by serum IgG) divided by (CSF Albumin divided by Serum Albumin) An IgG–albumin index is the ratio of CSF IgG:serum IgG divided by the CSF albumin:serum albumin ratio. Values greater than 0.85 indicate CSF IgG production, as seen in MS; or increased CSF production combined with increased permeability, as seen in CNS infections. MS is characterized by the presence of oligoclonal banding in the CSF in greater than 90% of patients with active disease. The total protein and myelin basic protein are often increased, and glucose is decreased. Reye syndrome results in hepatic failure, causing high CSF levels of ammonia and glutamine. CSF lactate is usually normal in patients with MS.

Answer 396

A A relative (percent) increase in PMNs may be significant even when the WBC count does not exceed the upper limit of normal. For this reason, a WBC differential using a concentrated CSF sample is always performed on neonates and when the WBC count is greater than 5/μL. Cytocentrifugation should be used to concentrate the cells followed by staining with the Wright stain.

Answer 397

C In newborns, the URL for WBCs is 30/μL (URL for adults is 5/μL) with the majority of WBCs being monocytes or macrophages. In normal neonates, monocytes (including macrophages and histiocytes) account for about 75% of the WBCs, lymphocytes for about 20%, and PMNs for about 3%. In normal adults, lymphocytes account for about 60% of the WBCs, monocytes for about 35%, and PMNs for about 2%.

Answer 398

D Neutrophils may appear in CSF as a result of many causes, making it necessary to correlate results of biochemical assays with hematologic findings. Low glucose and high protein levels occur in both malignancy and bacterial meningitis. Tumor markers and lactate may be helpful in distinguishing malignancy from bacterial meningitis. In neurosyphilis, there is usually an absolute lymphocytosis and increased total protein and IgG index

Answer 399

C Although the blood–brain barrier excludes most plasma proteins, abnormal serum proteins can cause parallel CSF electrophoretic patterns. Therefore, an abnormal CSF pattern indicates CNS disease only if not duplicated by the serum pattern. Normal CSF total protein in newborns may be up to two times higher than adult levels. Antibodies to T. pallidum remain in CSF after treatment, but nontreponemal antibodies disappear. Although the T. pallidum particle agglutination (TP-PA) test for specific antibodies is more sensitive, the Venereal Disease Research Laboratory (VDRL) test is often performed concurrently. A positive result for both tests is diagnostic of active tertiary syphilis.

Answer 400

D A culture should be performed on the sediment of the third aliquot of CSF after it is centrifuged. Blood and chocolate agar and anaerobic broth should always be used, and, if sterile, held for a minimum of 3 days. Blood cultures should be done because septicemia occurs in about one half of bacterial meningitis cases. Gram staining is always performed by using the sediment of the CSF because it is positive in more than 70% of acute bacterial meningitis cases. India ink, acid-fast, and wet preparations may be ordered if an absolute monocytosis is present.

Answer 401

B Group B Streptococcus and E. coli are the two most common isolates in neonates. H. influenzae, S. pneumoniae, and N. meningitidis are the most common isolates in children. S. pneumoniae is the most frequent isolate in older adults

Answer 402

C In cases of trauma, it may be necessary to differentiate rhinorrhea from CSF leakage, and this can be done by immunofixation electrophoresis to identify the tau protein found in CSF, but not in serum. Tau protein is an enzymatically modified form of transferrin that migrates in the slow beta zone just behind unmodified transferrin. Transthyretin or prealbumin is present in far greater concentration in CSF than in blood but may not be seen if CSF is diluted with nasal fluid. Myelin basic protein is a component of nerve sheaths and is present in CSF in about 60% of persons with MS. It is also found in persons with other demyelinating diseases, SLE, stroke, and brain injury. CRP is elevated in the CSF of approximately two thirds of persons with bacterial meningitis.

Answer 403

B Serous fluids include pleural, pericardial, and peritoneal fluids. They form from ultrafiltration of plasma through serous membranes. These are lined with specialized epithelium called mesothelium. They comprise about 5% of the cells in serous fluid and may be difficult to differentiate from malignant cells. Pleural fluid volume is normally less than 10 mL. The volume of pericardial fluid is normally 10 to 50 mL and peritoneal fluid 30 to 50 mL. Radiography can detect an increase in serous fluids of 300 mL or more. Normal serous fluids are clear and range in color from straw to light yellow

Answer 404

C Effusions are classified as either transudates, exudates, or chylous. Transudates result from abnormal hemodynamics (e.g., congestive heart failure, liver disease), and exudates and chylous fluids from local disease. Pleural fluid that is purulent is called empyemic fluid. Such fluid has a WBC count of 10,000/μL or greater.

Answer 405

C Transudative fluids are distinguished from exudative fluids by the physical appearance, cellularity, SG, total protein, LD, cholesterol, and bilirubin. Exudative fluids have a fluid:serum LD ratio greater than 0.6 caused by release of the enzyme from inflammatory or malignant cells. Exudative fluids have a total protein greater than 3.0 g/dL, SG greater than 1.015, fluid:serum total protein ratio greater than 0.6, cholesterol greater than 60 mg/dL (fluid:serum ratio greater than0.3) and fluid:serum bilirubin ratio greater than 0.6. Exudates are caused by infection, infarction, malignancy, rheumatoid diseases, and trauma

Answer 406

C Xanthochromia indicates either an exudative process or prior traumatic tap. Hemorrhagic pleural fluids usually have RBC counts greater than 100,000/μL and are usually caused by lung neoplasms. Clearing of fluid or diminished RBC counts in successive tubes favors a diagnosis of a traumatic tap. A clot may form in a hemorrhagic fluid or following a traumatic tap. However, a transudative fluid will not clot.

Answer 407

A Normal fluids have a WBC count less than 1,000/μL, but counts between 1,000 and 2,500/μL may be seen in both exudates or transudates. All WBC types are present, but no type should account for greater than 50% of the leukocyte count. An RBC count less than 10,000/μL is usually caused by a traumatic tap. A fluid hematocrit similar to blood is caused by a hemothorax. Pleural fluids containing greater than 100,000/μL RBCs are associated most often with malignancies but are also seen in trauma and pulmonary infarction

Answer 408

B Transudative fluids are caused by circulatory problems, usually decreased oncotic pressure or increased hydrostatic pressure. In contrast, exudative effusions are caused by inflammatory processes and cellular infiltration as seen in malignancy. In addition to an RBC count greater than 100,000/μL, malignancies often involve the lung, colon, breast, or pancreas and often produce carcinoembryonic antigen.

Answer 409

D Malignancy, pulmonary infarction, SLE, and RA are characterized by inflammation, with increases in protein, WBCs, and LD. Exudates can also be caused by tuberculosis, pancreatitis, and lymphoma. Lymphatic obstruction is often associated with lymphoma and other malignancies that block the flow of lymph into the azygous vein. This causes chylous effusions. Chylous effusions are also caused by traumatic injury to the thoracic duct. Necrosis causes a pseudochylous effusion. This resembles a chylous effusion in appearance but has a foul odor. Chylous fluids contain chylomicrons, stain positive for fat globules, show lymphocytosis, and have a triglyceride concentration over twofold higher than plasma (or greater than 110 mg/dL). Pseudochylous effusions are characterized by mixed cellularity and elevated cholesterol.

Answer 410

C Normal pleural fluid has the same glucose concentration as plasma. Hyperglycemia is the only condition that is associated with a high pleural fluid glucose. Low glucose levels (less than 60 mg/dL) may be seen in infection, malignancy, and rheumatic diseases. However, glucose levels are lowest (often below 30 mg/dL) and are a constant finding when rheumatoid disease affects the lungs. Pancreatitis causes an exudative peritoneal and pleural effusion with an elevated peritoneal fluid amylase (without a low glucose)

Answer 411

D The pH of pleural fluid is approximately 7.64, and values below 7.30 are usually associated with a poorer prognosis and usually require drainage. Esophageal rupture produces the lowest pH with values in the range of 6.0 to 6.3. In addition, pleural fluid pH is low in rheumatoid disease involving the lungs and pleura, some malignancies, and SLE. Low pH and glucose in pleural fluid are seen in lung abscesses and exudative bacterial pneumonia (called parapneumonic effusion). Pneumothorax results from air entering the pleural space and does not produce a low pH

Answer 412

A Peritoneal fluid normally has a WBC count less than 300/μL. Neutrophils should account for no more than 25% of the WBCs. A majority of PMNs indicates bacterial infection of the peritoneum. Lymphocytosis suggests malignancy, tuberculosis, cirrhosis, and lymphatic leakage. Peritoneal fluid amylase is elevated in most cases of acute pancreatitis. Peritonitis is suspected when the fluid LD is greater than 40% of the serum level. In contrast, normal pleural fluid has a WBC count usually less than 1,000/ μL. Exudative pleural fluids usually have a WBC count greater than 10,000/μL, but values tend to overlap noninflammatory fluids. The PMNs should comprise 50% of the WBCs or less, and the RBC count should be less than 100,000/μL. Lesser numbers are usually caused by a traumatic tap.

Answer 413

D Synovial fluid has approximately the same SG and glucose as plasma and the serous fluids but is far more viscous because of a high content of mucoprotein (hyaluronate) secreted by the synovium. Viscosity is estimated by pulling the fluid from the tip of a syringe or pipet. Normal fluid gives a string longer than 4 cm. Low viscosity indicates inflammation. The total protein of synovial fluid is usually lower than serous fluids, the URL being 2.0 g/dL.

Answer 414

A The WBC count is elevated in all types of arthritis but is greatest (50,000–100,000/ μL) in septic arthritis. Neutrophils comprise less than 25% of WBCs in normal and noninflammatory arthritis but are greater than 50% in inflammatory and septic arthritis. Fluids are diluted in saline because acetic acid causes a mucin clot to form. WBC counts should be performed within 1 hour of collection because the WBC count will diminish over time.

Answer 415

B Ragocytes are PMNs containing dark granules composed of immunoglobulins, but they may be seen in gout and septic arthritis as well as RA. LE cells may be seen in fluid from patients with SLE. Reiter cells, macrophages with ingested globular inclusions, are seen in Reiter syndrome and other inflammatory diseases

Answer 416

A Although all of the crystals mentioned can cause crystal-induced arthritis, uric acid and sodium urate crystals cause gout and are seen in about 90% of patients with gout

Answer 417

B Calcium pyrophosphate crystals occur as needles or small rhombic plates and can be confused with uric acid. They rotate plane polarized light but not as strongly as uric acid. Synovial fluid should never be collected in tubes containing powdered EDTA because it may form crystals that can be mistaken for in vivo crystals. The recommended anticoagulant is sodium heparin, although liquid EDTA may be used.

Answer 418

C Polarized microscopy with a red compensating filter differentiates uric acid from pseudogout crystals. When the long axis of uric acid needles is parallel to the slow vibrating light, the crystals appear yellow. When the long axis is perpendicular to the slow vibrating light, the crystals appear blue. Calcium pyrophosphate gives the reverse effect

Answer 419

C Synovial fluid glucose is normally less than 10 mg/dL below serum glucose, and should be collected after an 8-hour fast to ensure that the fluid and plasma are equilibrated. In septic arthritis, the glucose level is often greater than 40 mg/dL below the serum level and about 25 to 40 mg/dL lower in inflammatory arthritis, which includes gout. Osteoarthritis and hemorrhagic arthritis are not usually associated with low joint fluid glucose.

Answer 420

A Rheumatoid factor can be present in both serum and synovial fluids from patients with RA, SLE, and other inflammatory diseases. Rheumatoid factor is present in synovial fluid of approximately 60% of patients with RA. Normally, IgG in synovial fluid is about 10% of the serum IgG level. CH50 levels in serum and synovium are more differential. Both are increased in Reiter syndrome but are often low in SLE; synovial CH50 is decreased and serum CH50 is normal (or increased) in RA.

Answer 421

B Synovial fluid is normally sterile, and all of the organisms listed may cause septic arthritis. N. gonorrhoeae is responsible for about 75% of septic arthritis cases occurring in young and middle-aged adults. Staphylococcus is responsible for the majority of cases involving older adults and is the most frequently found isolate from infected joint replacements. Haemophilus spp., Staphylococcus spp., and Streptococcus spp. are the most common causes of arthritis in young children

Answer 422

A The WBC count of normal joint fluid is 200/μL or less. Values greater than 5,000/μL cause the fluid to be purulent and occur in septic arthritis, RA, and gout. WBC counts greater than 50,000 μL indicate septic arthritis. The majority of WBCs in normal fluid are monocytes, which usually account for 50% to 65%. Neutrophils and lymphocytes should account for no greater than 25% each. An increase in RBCs occurs in cases of infectious and hemorrhagic arthritis or results from a traumatic tap. Hemorrhagic fluid will appear turbid, red to brown, and often clotted. Inflammatory arthritis can allow fibrinogen to enter the fluid and thus clot. Fluid from a person with hemophilia will not clot in spite of the bloody appearance.

Answer 423

A Amniotic fluid bilirubin reflects the extent of fetal RBC destruction in cases of HDFN. The fluid is centrifuged and absorbance measured from 350 to 600 nm simultaneously by using a photodiode array detector. Background absorbance is corrected by constructing a baseline using the absorbances at 365 nm and 550 nm. The delta absorbance (∆A) of hemoglobin at 410 nm and of bilirubin at 450 nm is determined by subtracting the absorbance of the baseline from the respective peaks. Samples that are not grossly hemolyzed can be corrected for oxyhemoglobin by subtracting 5% of the ∆A at 410 nm from the ∆A at 450 nm. When hemolysis is severe or meconium is present, bilirubin must be extracted in chloroform before measuring absorbance. Bilirubin normally decreases with increasing gestational age because fetal urine contributes more to amniotic fluid volume as the fetus matures. The bilirubin concentration must be correlated with gestational age to correctly evaluate the severity of HDFN.

Answer 424

C Amniotic fluid bilirubin is the best index of the severity of HDFN and is measured by diode array spectrophotometry across the 365 to 550 nm range. When hemoglobin produces a positive slope at 410 nm, the bilirubin should be extracted with chloroform prior to scanning. Extraction methods give the best correlation with RBC destruction.

Answer 425

B Respiratory distress syndrome (RDS) develops when surfactants are insufficient to prevent collapse of the infant’s alveoli during expiration. Tests measuring pulmonary phospholipid surfactants are the most specific and sensitive indicators of RDS. An L/S ratio greater than 2:1 (in some laboratories 2.5:1) is the most widely accepted measure of FLM. Most of the surfactants in the amniotic fluid are present in the form of lamellar bodies. These can be counted using an electronic cell counter at the settings for enumerating platelets. Laboratories must correlate the LBC that corresponds to an LS ratio of 2:1. The LBC cutoff will differ depending on the counter.

Answer 426

A Pulmonary surfactants are mainly disaturated lecithins produced by type II granular pneumocytes. The L/S ratio increases toward the end of the third trimester because of increased production of lecithin. The concentration of sphingomyelin remains constant throughout gestation and serves as an internal reference. Meconium contains less lecithin than amniotic fluid and will usually decrease the L/S ratio; however, meconium produces a spot that can be misinterpreted as lecithin, leading to a falsely increased L/S ratio. Sufficient PG to produce a spot is seen only when the L/S ratio is 2:1 or higher. PG is not present in either blood or meconium, and therefore, its presence indicates fetal lung maturity. In diabetes, the fetal lungs may mature more slowly than normal, and infants may develop RDS when the L/S ratio is 2:1 or slightly higher. For this reason, an L/S of 3:1 more closely correlates with fetal lung maturity when testing amniotic fluid from mothers with diabetes. As in all other cases, when the amniotic fluid from a diabetic mother is positive for PG, fetal lung maturity is established.

Answer 427

C Pulmonary surfactants are largely present in the form of lamellar bodies and can be lost by centrifuging the amniotic fluid at high g force. Centrifuge speed should be the minimum required to spin down cells (450 g for 10 minutes at 4°C). Samples that cannot be measured immediately should be refrigerated or frozen. Samples are stable for up to 3 days at 2°C to 8°C and for months when frozen at –20°C or lower. Meconium and blood may also introduce errors when measuring the L/S ratio. Blood has an L/S ratio of approximately 2:1 and will falsely raise the L/S ratio when fetal lungs are immature and depress the L/S ratio when fetal lungs are mature.

Answer 428

B In normal pregnancy, hCG levels rise exponentially following implantation and peak at weeks 9 to 12, reaching in excess of 100,000 mIU/mL. The hCG doubling time averages 2.2 days. In ectopic pregnancy, the expected increase between consecutive days is below normal. Levels fall after the first trimester to about 20,000 mIU/mL and then remain at about that level through term. Hydatiform moles are associated with greatly elevated levels of hCG. Serum hCG can take up to 4 weeks to return to nonpregnant (less than 25 mIU/mL) or baseline (less than 5 mIU/mL) levels following delivery, stillbirth, or abortion.

Answer 429

C The α-subunit of hCG is very similar to the α-subunit of TSH and FSH and identical to LH. Although the β-subunits of hCG and LH are very similar, antibodies can be made to the β-subunit of hCG that do not cross-react with LH or other pituitary hormones. Most enzyme immunoassay (EIA) methods utilize two monoclonal antibodies against different sites of the hCG molecule. One antibody is specific for the carboxy terminal end of the β-chain, and the other reacts with the α-chain, resulting in a positive test only when intact hCG is present. Because monoclonal antibodies are usually derived from mouse hybridomas, rare false-positive results may occur in patients who have anti-mouse immunoglobulin antibodies. Although the test can detect lower levels of hCG, 25 mIU/mL is the positive cutoff for pregnancy. Serum is preferred over urine because serum levels are more consistently above the cutoff compared with random urine in very early pregnancy

Answer 430

C Assays of intact hCG are double antibody sandwich immunoassays. One antibody reacts with the α-subunit and the other with the β-subunit. In assays where both antibodies are added together, a process called the “hook effect” is known to occur. In extreme antigen excess, the hCG saturates both antibodies, preventing sandwich formation. This results in measurement of falsely low levels of hCG

Answer 431

A Estriol is produced by the placenta as well as the fetal and maternal adrenal glands and liver. Free estriol produced by the placenta is rapidly conjugated by the maternal liver. Almost all of maternal serum unconjugated (free) estriol is derived from the fetus and is a direct reflection of current fetal placental function. Serum unconjugated estriol (uE3) measured during the second trimester is used along with serum AFP, hCG, and dimeric inhibin A as part of the quad marker screening test for Down syndrome. AFP and uE3 are decreased by approximately 25%, inhibin A is increased by a factor of approximately 1.8, and hCG is increased by a factor of approximately 2.5 in Down syndrome pregnancies. When all four assays are combined with adjustments for maternal age, gestational age, race, maternal weight, and diabetes, the detection rate is approximately 70% to 80% and the false-positive rate 7%.

Answer 432

A Maternal serum AFP increases steadily until 2 months prior to full term as AFP passes from the fetal urine into the amniotic fluid. Because serum levels are dependent on gestational age, URLs depend on the date of the last menstrual period. AFP is measured between 14 and 18 weeks gestation, and levels are reported as multiples of the median to permit interlaboratory comparison. When serum levels are high, ultrasonography is used to determine fetal age and rule out twins. Increased maternal serum AFP levels (greater than 2.5 MoM) may result from many diseases in addition to open neural tube defects, such as spina bifida. These include anencephaly, ventral wall defects, congenital hypothyroidism, and Turner syndrome. Decreased levels (less than 0.75 MoM) may be seen in approximately 25% of Down syndrome pregnancies

Answer 433

B Maternal serum AFP levels are too low to measure accurately during the first trimester, and intact hCG and estriol do not discriminate well between 21 trisomy pregnancy and normal pregnancy before the second trimester. First trimester screening for Down syndrome (and trisomy 18) can be performed between weeks 10 and 13 by using free β-hCG (almost twofold higher in Down syndrome) and pregnancy- associated plasma protein A (PAPP-A) which has a median in Down syndrome less than half of that seen in normal pregnancy. These two markers used together with high-resolution ultrasonography to determine nuchal fold thickness (swelling at the base of the neck) have a sensitivity of 85% to 90%. Nuchal fold thickness (NT) in Down syndrome averages 1.5 MoM compared with 1.0 MoM for normal pregnancy.

Answer 434

B Reporting of screening markers as MoM has two advantages: (1) It eliminates interlaboratory variation in reference ranges seen when concentration units are reported. Laboratories using different methods (antibodies or calibrators) may have significantly different mass unit results for the same sample, necessitating different reference ranges. (2) The reference range in concentration units is also dependent on the gestational age at the time of sample collection; however, the average result for normals is always 1.0 MoM, regardless of the gestational age of the cohort. Use of MoM obviates the need to report specific reference ranges based on method or gestational age and makes calculation of risk less complicated.

Answer 435

B Down syndrome can result from a 14–21 translocation or isochromosome formation, but most cases arise from nondisjunction of chromosome 21 during meiosis. Plasma cell free DNA testing can be done as early as week 10 and detects fetal DNA released from fetal cells that has crossed the placenta. The test measures the ratio of fetal DNA:maternal DNA from chromosomes X, Y, 13, 18, and 21 with use of single nucleotide polymorphisms on the respective chromosomes to distinguish fetal DNA from maternal DNA. This ratio can be misinterpreted if more than one fetus is present. If any screening test is positive, amniocentesis or chronic villus sampling is performed, and trisomy is investigated by using chromosome karyotyping, microarray, or fluorescence in situ hybridization (FISH) on fetal cells

Answer 436

B The fetal fibronectin test is used mainly to rule out the likelihood of preterm delivery in high-risk pregnancies or in women with signs of preterm labor. Fetal fibronectin is a basement membrane protein produced by the amnion and chorion. It is present in cervical secretions in early pregnancy but disappears by about week 20. When there is inflammation to the membranes preceding delivery, fibronectin is released and can be found in cervicovaginal secretions. A positive test (greater than 50 ng/mL) has a sensitivity of about 60% in predicting preterm birth. However, a negative test has a 92% negative predictive value for the likelihood of preterm delivery and effectively rules out preterm delivery within the next 2 weeks. Amniotic fluid that has escaped from ruptured membranes is identified by testing a vaginal swab for pH. Vaginal fluid is normally acidic, with a pH between 5.0 and 6.0. After rupture of the membranes, the pH of the fluid changes to 6.5 to 7.5. This change can be detected by using Nitrazine paper or a swab containing Nitrazine yellow.

Answer 437

C Spermatozoa have a well-defined headpiece consisting of the acrosome and nucleus. The acrosome comprises the anterior portion of the head and contains nutrients and enzymes needed for penetration of the ovum. A thin filament, the neckpiece, connects the head and tail. The tail is divided into the midpiece, principal piece (mainpiece), and endpiece. The midpiece is the thick anterior end of approximately 5 μ. It contains a 9 × 2 + 2 longitudinal arrangement of microtubules (two central microtubules surrounded by nine doublets so that a cross section resembles a pinwheel). This is called the axoneme and it is surrounded radially by nine outer dense fibers which in the midpiece are covered by a sheath containing mitochondria. The longest portion of the tail (40–45 μ) is the principal piece. Its axoneme is thinner than the midpiece. The distal portion, called the endpiece, is approximately 5 μ. It contains the axoneme but is unsheathed

Answer 438

C Varicocele is the hardening of veins that drain the testes. This causes blood from the adrenal vein to flow into the spermatic vein. Adrenal corticosteroids retard the development of spermatozoa. Mumps, Klinefelter syndrome, and malignancy cause testicular failure, which accounts for about 10% of infertility cases in men

Answer 439

A The reference range for spermatozoa is 15 to 150 × 10^6/mL. Concentrations below 15 × 10^6/mL are considered abnormal. The sperm concentration is multiplied by the seminal fluid volume to determine the sperm count. The lower limit of normal for the sperm count is 40 × 10^6 per ejaculate. This often results from obstruction of the ejaculatory duct or testicular failure.

Answer 440

A Acrosomal deficiency, nuclear abnormalities, and lengthened neckpiece are the most common morphological abnormalities of spermatozoa. Tapering of the head is a nuclear abnormality. Sperm morphology should be evaluated by classifying 200 mature sperm in duplicate by strict criteria. There are several strict criteria in use. The normal sperm head is approximately 4.0 to 5.0 μm in length, 2.5 to 3.5 μm in width, has an L/W ratio of 1.3 to 1.8, and an acrosomal area of 40% to 70%. Using strict criteria, there is a high likelihood of infertility when the number of normal forms is below 4%.

Answer 441

A Eosin Y is excluded by living sperm and is used to determine the percentage of living cells. Papanicolaou, Giemsa, and hematoxylin stains are used to evaluate sperm morphology. The viability test should be performed whenever the results of the motility test are subnormal

Answer 442

A The normal volume of seminal fluid is 1.5 to 5.0 mL. A lower volume than 1.5 mL causes a low sperm count (sperm/mL × volume) and can be caused by absence of the seminal vesicles or prostate, ductal obstruction, or retrograde ejaculation of seminal fluid into the urinary bladder. The seminal fluid should coagulate within 5 minutes after ejaculation because of secretions of the seminal vesicles. Proteases, such as prostate-specific antigen (PSA) hydrolyze semenogelin and fibronectin, causing liquefaction to occur within 1 hour at room temperature. The seminal fluid pH should be between 7.2 and 8.0. Motility is evaluated by grading the movement of two replicates of 200 sperm in five high-power fields. It is normal when 32% or greater show progressive movement or when 40% or greater show progressive and nonprogressive movement.

Answer 443

B A seminal fluid sample should not be collected following coitus. The patient should abstain from ejaculation for at least 2 days but no more than 7 days prior to submitting the sample. A condom should not be used because it may contain spermicides. The sample should be collected at the testing site in a sterile jar with a wide opening, and stored at room temperature. The specimen should be analyzed as soon as possible. The time between collection and delivery to the laboratory must be documented. Motility should be determined as soon as the fluid has liquefied (maximum storage time is 1 hour). Anticoagulants are not used; if the sample fails to liquefy, it can be treated with chymotrypsin before analysis

Answer 444

A When evaluating sperm morphology, the number of round cells (immature spermatozoa and WBCs) should also be determined. The number of each is counted along with 200 mature sperm and then divided by 2 to determine their percentage. This is multiplied by the sperm concentration to give the absolute count per milliliter. An increased number of WBCs is an indicator of infection and is usually associated with prostatitis. Round cells are also estimated by noting their number per high-power field. Each round cell per field counted with the 40× objective corresponds to one million per milliliter. The upper limit of normal for WBCs is 1 × 10^6/mL and for immature sperm 5 × 10^6/mL.

Answer 445

C Fructose is the primary nutrient in the seminal fluid and is needed for motility. It is supplied by the seminal vesicles and is low when the vas deferens or seminal vesicles are absent. The lower limit of normal is 150 mg/dL, or 13 μmol, per ejaculate.

Answer 446

B Peptic ulcer disease may be caused by either gastric or duodenal ulcers, which are associated with discomfort, hyperacidity, and bleeding. Hyperacidity is most often caused by H. pylori infection, which can cause both gastric and duodenal ulcers. In the absence of a positive test for H. pylori (e.g., endoscopic biopsy, breath test, enzyme- linked immunosorbent assay [ELISA], polymerase chain reaction [PCR]) and no history of drug induced ulcers, Z-E syndrome (gastrinoma) should be suspected, and can usually be identified by a plasma gastrin assay. Cancer of the stomach is associated with increased gastric fluid volume but not hyperacidity. Pernicious anemia is associated with gastric hypoacidity, and not ulcers.

Answer 447

C Gastrin is produced by specialized epithelium of the stomach and stimulates secretion of HCl by parietal cells. Secretion is controlled by negative feedback causing levels to be high in conditions associated with achlorhydria, such as atrophic gastritis. Z-E syndrome results from a gastrin-secreting tumor, gastrinoma, usually originating in the pancreas. It is characterized by very high levels of plasma gastrin and excessive gastric acidity. In duodenal ulcers, increased gastric acidity occurs, but fasting plasma gastrin levels are normal. However, postprandial gastrin levels may be elevated in these patients because they do not respond to the negative feedback signal caused by HCl release. In stomach cancer, gastric volume is increased but acidity is not, and plasma gastrin levels are variable.

Answer 448

C Gastric analysis is performed rarely because endoscopic procedures usually are sufficient to diagnose hypo- and hyperacidity states. In difficult cases, analysis of gastric fluid can be used to make a definitive diagnosis. Free HCl in gastric residue from a 12-hour fasting sample obtained by nasogastric suction is measured by titrating with 0.1 N NaOH to a pH 3.5. Total acidity is titrated to pH 7.0, and includes contributions of other acids, including proteins and salts of chloride. Basal acid output (BAO) and peak acid output (PAO) are determined by using timed collection of gastric sample aliquots before and after stimulation of HCl release by pentagastrin. In achlorhydria, the fasting gastric pH is often greater than 6.0, and this is considered diagnostic. The BAO:PAO ratio is normally less than 0.2. Patients with gastric ulcers may also have a ratio less than 0.2 or between 0.2 and 0.4. In duodenal ulcers, the ratio is usually between 0.2 and 0.6. The ratio is greater than 0.6 only in Z-E syndrome.

Answer 449

A Plasma gastrin levels greater than 1,000 pg/mL are usually diagnostic of Z-E syndrome. Smaller elevations can occur in other types of hyperacidity, including gastric ulcers, in renal disease, and after vagotomy. Z-E syndrome can be differentiated from the others by using the secretin stimulation test. Secretin is administered intravenously, and timed plasma samples are collected and measured for gastrin. In Z- E syndrome, at least one specimen should show an increase of 200 pg/mL above the baseline for gastrin. Cholecystokinin–pancreozymin (CCK-PZ), a hormone produced by the small intestine, stimulates HCl production in the stomach, pancreatic release of bicarbonate, and intestinal motility. It may be measured to diagnose intestinal malabsorption, or used along with tests of other gastric regulatory peptides to evaluate dysfunction. Trypsinogen is a precursor of trypsin and is produced by the pancreas. Urinary trypsinogen is increased in acute pancreatitis, whereas fecal trypsin and chymotrypsin are decreased in cystic fibrosis because of pancreatic duct obstruction

Answer 450

B The xylose absorption test differentiates pancreatic insufficiency from malabsorption syndrome (both cause deficient fat absorption). Xylose is absorbed by the small intestine without the aid of pancreatic enzymes. It is not metabolized and is excreted into urine. Low levels indicate gastrointestinal malabsorption.

Answer 451

A Blood in feces is a very sensitive indicator of gastrointestinal bleeding and is an excellent screening test to detect asymptomatic ulcers and malignancy of the gastrointestinal tract. However, the test is nonspecific and contamination with vaginal blood is a frequent source of error.

Answer 452

C Digestive enzyme tests are used to identify infants and children with pancreatic insufficiency as a consequence of cystic fibrosis, and adults who have chronic pancreatitis. Such tests include fecal trypsin and chymotrypsin, serum immunoreactive trypsin, serum lipase, and fecal elastase-1. Fecal chymotrypsin is somewhat more sensitive in diagnosing pancreatic insufficiency and chronic pancreatitis than fecal trypsin or serum immunoreactive trypsin, but the most sensitive and specific enzyme test is fecal elastase-1, which is low in about 90% of persons with cystic fibrosis as well as pancreatic insufficiency and in greater than 75% of adults with moderate to severe chronic pancreatitis. Lipase is neither sensitive nor specific for chronic pancreatitis.

Answer 453

C Highly buffered alkaline urine may cause a false-positive result on the dry reagent strip protein test by titrating the acid buffer on the reagent pad. Protein should be measured by an alternate method that is not subject to positive interference by highly buffered alkaline urine.

Answer 454

C A positive nitrite result requires infection with a nitrate-reducing organism, dietary nitrate, and incubation of urine in the bladder. The test is positive in about 70% of UTI cases. Alkaline pH, bacteriuria, and leukocytes point to UTI.

Answer 455

B This discrepancy between the blood reaction and RBC count resulted from spinning less than 12 mL of urine. When volume is below 12 mL, the sample should be diluted with saline to 12 mL before concentrating. Results are multiplied by the dilution (12 mL/mL urine) to give the correct range.

Answer 456

A Ammonium urate crystals occur at alkaline pH only. The pH should be checked, and if it is below 7.0, the crystals should be reviewed for correct identification. The trace ketone does not require confirmation, provided that the quality control of the reagent strips is acceptable.

Answer 457

A Bilirubin crystals cannot occur in urine without bilirubin. The dry reagent strip test should be repeated, and if the result is negative, a new specimen should be requested as bilirubin may have degraded due to storage. If a second sample yields a negative result, the crystals should be reviewed before reporting. Abnormal crystals occur only in acid or neutral urine

Answer 458

D Patients with prerenal failure usually have a BUN:creatinine ratio greater than 20:1. Reduced renal blood flow causes increased urea reabsorption and high urine osmolality. Patients are usually hypertensive and show fluid retention and hyperkalemia.

Answer 459

A Urine glucose concentration is dependent on blood glucose concentration at the time urine is formed. The postprandial glucose (2 p.m.) level exceeded the renal threshold, resulting in trace glycosuria. Tests for reducing sugars are not used to confirm a positive urine glucose test result.

Answer 460

C RBCs usually remain intact at a SG of 1.015. The absence of RBCs, WBCs, and casts points to hemoglobinuria caused by intravascular hemolysis rather than glomerular injury. A positive protein reaction will occur if sufficient hemoglobin is present.

Answer 461

D The plasma free hemoglobin will be increased immediately after a hemolytic transfusion reaction, and the haptoglobin will be decreased. The hemoglobin will be eliminated by the kidneys, but the haptoglobin will remain low or undetectable for 2 to 3 days. Normal urine urobilinogen and serum unconjugated bilirubin help in ruling out extravascular hemolysis. Pretransfusion potassium is needed to evaluate the contribution of hemolysis to the post-transfusion result.

Answer 462

B The combination of glucose and ketone positivity of urine points to a patient with insulin-dependent diabetes. A false-positive SSA test result is likely if tolbutamide (Orinase) has been administered

Answer 463

A A nonhemolyzed trace may have been overlooked and the blood test should be repeated. A false-negative result (e.g., megadoses of vitamin C) rarely occurs. Yeast cells often accompany pyuria and glycosuria and are easily mistaken for RBCs.

Answer 464

C At pH 6.5, amorphous crystals are most often urate. These form yellow- or reddish- brown refractile deposits sometimes resembling blood or granular casts. The number of blood casts reported could not have occurred with negative protein and blood test results.

Answer 465

B When RBCs pass through the damaged endothelial wall of the glomerulus, they become distorted, and such cells are described as dysmorphic in appearance. They are characterized by uneven distribution of hemoglobin, cytoplasmic blebs, and an asymmetrical membrane distinct from crenation. The cytoplasm may be extruded from the cell and may aggregate at the membrane giving the cell a wavy appearance. A predominance of dysmorphic RBCs in the microscopic examination points to glomerular bleeding as opposed to hematuria from other causes. Intravascular hemolytic anemia causes hemoglobinuria, rather than hematuria. RBCs lyse in hypotonic and alkaline urine. Severe dehydration is not a cause of hematuria.

Answer 466

C Urinary urobilinogen is increased in persons with extravascular hemolysis or hepatocellular liver disease. A freshly voided specimen is needed to detect urobilinogen because it is rapidly photo-oxidized to urobilin. This is accompanied by a color change from orange to brown. Urobilin does not react with 2,4 dimethylaminobenzaldehyde or 4-methoxybenzene diazonium tetrafluoroborate, which are used to detect urobilinogen. Consequently, the urobilinogen test in the first sample will be normal but will be increased in the second sample if tested immediately after collection. The best sample for detecting urobilinogen is a 2-hour timed urine sample collected in the midafternoon, when urobilinogen excretion is highest. Ketones and nitrites do not alter the pigment of the urine sample. Leukocytes cause the urine to be turbid but do not cause abnormal color. These three tests are stable for 24 hours when urine is refrigerated within 30 minutes of collection.

Answer 467

C Protein and other constituents of urine will often be highest in the first morning void. A normal first-voided sample makes glomerular disease highly unlikely. Orthostatic albuminuria is a benign condition sometimes seen in adolescents who are tall and have a bent posture that puts back pressure on the kidneys. The quantity of albumin excreted into the urine is small. Diagnosis is made by demonstrating a positive test after the person is erect for several hours, and the absence of proteinuria when the person is recumbent. Microalbuminuria seen in persons with diabetes is usually accompanied by a positive test result for urinary glucose.

Answer 468

C RBCs will lyse in alkaline or dilute urine, and this sample displays both. The blood test is sensitive to as little is 0.015 mg/dL hemoglobin, and the protein test is significantly less sensitive. As a result, trace to small positive blood and negative protein are commonly encountered

Answer 469

A When 5 to 10 RBCs/HPFs are seen, the blood test should show a nonhemolyzed trace. Therefore, it is likely that the cells are not RBCs. RBCs are easily confused with nonbudding yeast and may also be mistaken for WBCs. RBCs will lyse in dilute acetic acid, but yeast and WBCs will not. If a yeast infection is present, then the leukocyte esterase test result will likely be positive; therefore, the leukocyte esterase test cannot be used to determine the identity of the cells. The Sternheimer-Malbin stain can be used to differentiate WBCs from RBCs and yeast.

Answer 470

D A differential is performed by using CSF concentrate on all neonatal samples and whenever the WBC count is greater than 5μL. A toluidine blue chamber count of PMNs is not sufficiently sensitive to detect neutrophilic pleocytosis.

Answer 471

A A traumatic tap makes classification of fluids difficult on the basis of cell counts and protein. The values reported for protein, RBCs, and WBCs can occur in either an exudate or bloody transudate, but the LD ratio is significant.

Answer 472

A Chylous effusions are caused by extravasation of lymphatic fluid into the pleural cavity. Pseudochylous effusions are caused by necrosis. Both fluids often appear white and opalescent, but both effusions can also be bloody, green, or yellow, in addition to being turbid. However, chylous effusions are odorless and have a twofold higher triglyceride compared with plasma. They also usually show a lymphocytosis. Pseudochylous effusions are foul smelling and usually have a mixed cellularity and an elevated cholesterol. These effusions may have triglyceride, but it is usually below 50 mg/dL. Chylous effusions are most often caused by lymphoma or other malignancy or trauma, and, like pseudochylous effusions, may have an increased LD fluid:serum ratio, total protein, and WBC count.

Answer 473

D CSF glucose is approximately 60% of the plasma glucose but may be somewhat lower in a person with diabetes. The reference range is approximately 40 to 70 mg/dL. A CSF glucose level above 70 mg/dL is caused by a high plasma glucose that equilibrated with CSF. Therefore, hyperglycorrhachia is caused by hyperglycemia. The WBC count in a child between 5 and 12 years of age is 0 to 10 × 10^6/L (0–10/μL). The normal RBC count and protein rule out subarachnoid hemorrhage and traumatic tap. Although aseptic meningitis cannot be ruled out conclusively, it is unlikely given a normal WBC count and IgG index.

Answer 474

A Bloody, exudative fluids with a preponderance of a singular cell type are suggestive of malignancy. The cellularity in malignancy is variable but lymphocytosis occurs in about half the cases. Mesothelial cells normally comprise less than 10% of the cells in serous fluid. They may be resting cells, reactive, degenerated, or phagocytic in nonmalignant conditions. In inflammatory conditions, they are often increased and resemble macrophages. However, clusters or balls of such cells and paper-punch vacuoles throughout the cytoplasm and over the nucleus are characteristics of malignant mesothelial cells. Such cells secrete hyaluronic acid, making the fluid highly viscous. The gross appearance of this fluid suggests malignancy. The description of these cells points to mesothelioma, and this specimen should be referred for cytological examination to confirm the diagnosis.

Answer 475

C A calculated clearance in excess of 140 mL/min is greater than the upper physiological limit. The high volume per day suggests addition of H2O, or urine that should have been voided and discarded at the start of sample collection. The result should be considered invalid.

Answer 476

D Serum amylase peaks 2 to 10 hours after an episode of acute pancreatitis, and this may have caused the elevated serum amylase at 8 p.m. Urinary amylase parallels serum amylase; therefore, a positive urine test at 6 p.m. makes sample collection error unlikely.

Answer 477

A In patients with poorly controlled diabetes, lung maturity may be delayed and an L/S ratio of 2:1 may be associated with respiratory distress syndrome. A positive PG spot correlates with an L/S ratio of 2:1 or higher and rules out a falsely increased result caused by blood contamination. However, the appearance of PG in amniotic fluid is often delayed in diabetes. The best course of action is to wait an additional 24 hours and perform another L/S ratio on a fresh sample of amniotic fluid because an L/S ratio of 3:1 would indicate a high probability of lung maturity.

Answer 478

C Urine creatinine of less than 0.8 g/day indicates incomplete sample collection. The patient’s daily catecholamine excretion would be misinterpreted from this result.

Answer 479

C Sperm motility should be performed in duplicate and 200 cells per sample in several fields should be evaluated for movement. Agreement between duplicates must be within a specified percentage based on the category with the highest percentage. In this case, progressive movement is highest at 50%, and the difference between replicates should be no greater than 10%

Answer 480

A hCG may be produced in men by tumors of trophoblastic origin, such as teratoma and seminoma, and is an important marker for nontrophoblastic tumors, as well

Answer 481

B Lamellar bodies are small particles containing pulmonary surfactants that are made by type II pneumocytes, and their number in amniotic fluid increases as the concentration of phospholipids increases. They are about the same size as platelets and are counted in the platelet channel of cell counters. If the amniotic fluid sample is contaminated with blood, platelets will falsely raise the LBC. Amniotic fluid samples for LBC are stable for several days when stored at 4°C. However, cutoffs for FLM need to be established by each laboratory because there are significant differences in LBCs between different counters.

Answer 482

B Tampering with a sample submitted for abuse substance testing can be either by dilution or substitution. Substance Abuse and Mental Health Services Administration (SAMHSA) certified workplace drug testing laboratories are required to test for both, and reject samples based on SAMHSA cutoffs. A specimen is too dilute for testing if the creatinine is less than 20 mg/dL and SG below 1.003. A sample is considered substituted if creatinine is less than 5.0 mg/dL and SG less than 1.002. Values in A and C for pH and temperature are within acceptable limits.

Answer 483

C Urine validity testing for drugs of abuse includes tests for nitrite, glutathione, pyridinium dichromate, and peroxide in addition to pH, SG, and creatinine. These substances are known to cause negative interference in the enzyme-multiplied immunoassay technique (EMIT test). A viral infection of the kidney would be associated with high numbers of renal tubular epithelial cells and leukocytes. An infection in an immunosuppressed person would still produce urinary WBCs. Although laboratory error is possible, a false-positive result caused by reflectometer error would be suspected if the test pad were negative when reading it manually.

Answer 484

C Although the sample is still suitable for microbiological analysis, it will not give reliable cell counts or biochemistry results because of extensive contamination with peripheral blood

Answer 485

B Joint fluid too viscous to pipet accurately cannot be diluted accurately. Complement is heat labile, and total hemolytic complement is destroyed when the sample is heated to 56°C for 5 minutes. Joint fluid is difficult to collect, and a new sample is likely to have the same problem.

Answer 486

A Cellular distortion caused by centrifugation is a common problem and can be reduced by adding 22% bovine albumin or 10% dextran to the cytospin cup along with the sample. In the absence of a large subarachnoid hemorrhage, CSF does not clot because it contains no fibrinogen, and the sample can be collected and counted without anticoagulant.

Answer 487

A Electronic cell counters are validated for body fluid cell counts with specific minimum detection limits. For most counters, this is 50 to 200 total nucleated cells (TNCs)/μL and 10,000 RBC/μL. Specialized counters using fluorescent and image analysis can achieve low end sensitivities for both TNC and RBC counts of 0 to 1/μL. Because the RBCs are lysed in the WBC bath, the WBC count represents the number of nucleated cells present. When cell counters that perform CBCs are used, the WBCs are not lysed in the RBC bath and would be counted as RBCs. In this case, the empyemic fluid would cause the RBC count to be erroneously elevated, and this should be corrected before reporting by subtracting the WBC count from the RBC count