RBC disorders Flashcards
1
Q
Anemia is defined as a reduction in
A
red cell mass, with consequent decrease in oxygen transport capacity of the blood.
2
Q
Clinical parameters used in testing for anemia include
A
red cell count, hemoglobin concentration, and hematocrit, all of which reflect, but do not directly measure, the red cell mass.
3
Q
Accepted “normal” RBC levels vary with
A
age, sex, and geographic location.
4
Q
Clinically, anemia results in impaired
A
tissue oxygenation as manifest by exertional shortness of breath, weakness, fatigue, and pallor.
5
Q
Polycythemia denotes an
A
increase in red cell mass.
6
Q
Anemias can be classified into three broad categories based on the mechanism by which red cell mass is decreased:
A
blood loss, decreased red cell production, and decreased red cell survival.
7
Q
Other Anemia classification systems based on
A
red cell morphology are also in common use.
8
Q
RBC (Blood) Loss
A
Hemorrhage
Trauma (acute)
GI or GYN disease
9
Q
Decreased RBC Survival
A
Mechanical trauma transfusion reactions hereditary spherocytosis hemoglobinopathies thalassemias G6PD deficiency Erythroblastosis fetalis Malaria
10
Q
Decreased RBC Production
A
Iron deficiency anemia Vitamin B12 deficiency Folate deficiency Aplastic anemia Myelophthisic anemias
11
Q
Young healthy subjects can tolerate rapid blood loss of
A
500-1000 mL (up to 15-20% of total blood volume) with few symptoms, but some will have a vasovagal response- sweating, weakness, nausea, slow heart rate, hypotension.
12
Q
If blood loss is controlled, interstitial fluid will
A
redistribute (within 24 hours) into the vascular space in an attempt to re-expand the vascular volume.
13
Q
Loss of 1000-1500 mL produces
A
lightheadedness, orthostatic hypotension;
14
Q
with loss of 1500-2000 mL, all patients are
A
symptomatic- thirst, shortness of breath, loss of consciousness, sweating, rapid pulse, decreased blood pressure, clammy skin.
15
Q
Rapid loss of 2000-2500 mL produces
A
shock.
16
Q
The loss of RBC stimulates
A
increased production, mediated by erythropoietin, resulting in an increase in the reticulocyte count in the peripheral blood.
17
Q
Chronic blood loss causes anemia when the rate of loss
A
exceeds the capacity for RBC regeneration or when iron reserves are depleted.
18
Q
Chronic GI hemorrhage due to ulcer or neoplasm, or GYN hemorrhage (menorrhagia) are important causes of
A
iron deficiency.
19
Q
Hemolytic anemias are characterized by
A
shortened red cell survival and retention of products of red cell destruction (iron).
20
Q
Increased erythropoietin production results in increased
A
red cell production with a reticulocytosis to compensate for the anemia.
21
Q
Red cell destruction can occur within the
A
circulation (intravascular hemolysis) or in the reticuloendothelial system including spleen (extravascular hemolysis).
22
Q
Intravascular hemolysis: destruction of
A
RBC within the circulation. Examples: mechanical trauma (e.g., from a defective heart valve), hemolytic transfusion reaction.
23
Q
Hemoglobin released from RBC into circulation (hemoglobinemia) is bound to
A
haptoglobin, a binding protein, and cleared from the circulation by the liver.
24
Q
A decrease in serum haptoglobin is a key feature of
A
intravascular hemolysis.
25
When plasma hemoglobin levels exceed amount of available haptoglobin, free hemoglobin is
excreted in the urine (hemoglobinuria); however hemoglobin is toxic to the kidney, and iron that accumulates in proximal tubular cells in the kidney as a breakdown product of hemoglobin is lost in the urine when these cells are shed (hemosiderinuria).
26
Conversion of heme (derived from hemoglobin) to bilirubin leads to
hyperbilirubinemia and jaundice. The degree of jaundice is dependent on the functional capacity of the liver and rate of hemolysis. Levels of haptoglobin are characteristically low.
27
Intravascular hemolysis: • Immune
| –
Transfusion reaction
28
Intravascular hemolysis: • Non-immune
– Mechanical trauma (defective heart valve)
29
Extravascular hemolysis: destruction of RBC in
reticuloendothelial system (spleen, liver). Examples: Hereditary spherocytosis, sickle cell anemia, erythroblastosis fetalis (antibody-mediated hemolytic disease of the newborn).
30
Damaged or abnormal RBC are removed in
spleen, where hemoglobin is broken down intracellularly.
31
Free hemoglobin is not released from spleen directly into
the blood and urine, but hemoglobin breakdown products are increased (hyperbilirubinemia) and jaundice may result.
32
Spleen and liver may become enlarged since these are sites of
removal of RBC from the circulation.
33
Chronically elevated levels of bilirubin can promote formation of
gallstones.
34
Hemolytic anemias are classified by the mechanism of
red cell destruction into intrinsic defects (hemoglobin production, membrane abnormality) which are usually inherited, and extrinsic defects (antibody, mechanical trauma) which are usually acquired abnormalities.
35
Intrinsic: Membrane defects: Example: hereditary spherocytosis –
extravascular hemolysis. An inherited defect in the red cell membrane results in less deformability of RBC, so that they are sequestered and destroyed in the spleen.
36
Hereditary spherocytosis: The specific defect can be a qualitative or quantitative deficiency of
spectrin, a structural protein of the cytoskeleton.
37
Hereditary spherocytosis is ---------------- inheritance in most cases.
Autosomal dominant
38
Hereditary spherocytosis: Manifest in
adult life, severity is variable.
39
Hereditary spherocytosis: Removal of spleen results in
normal red cell survival but not normal red cell morphology. Production of spherocytes continues, but following splenectomy their destruction is decreased
40
Abnormal hemoglobin: Example: sickle cell anemia –
extravascular hemolysis. An inherited defect (autosomal codominant) in the structure of globin chain causes hemoglobin to gel upon deoxygenation.
41
Sickle cell: The specific defect is a
single base pair substitution in DNA that causes a single amino acid substitution (valine for glutamic acid) at position 6 in the beta chain of globin to produce sickle hemoglobin (HbS).
42
Sickle cell: Under low oxygen conditions the abnormal hemoglobin
polymerizes, causing the RBC to assume a "sickle" shape.
43
Sickle cell: The sickled cells are rigid and vulnerable to
splenic sequestration (decreased survival), and can also block the microcirculation causing ischemia and/or infarction.
44
Sickle Cell: Sickle cell disease occurs in
homozygotes for HbS, and is characterized by severe anemia, and vaso-occlusive crises, including acute chest syndrome and stroke.
45
Sickle cell: Complications may also include
autosplenectomy, painful crises, leg ulcers, retinal and renal thromboses.
46
About 8% of blacks in USA have
sickle cell trait (heterozygotes), and are essentially asymptomatic because less than half of the hemoglobin is abnormal and the concentration of HbS within the RBC is insufficient to cause sickling.
47
There is a Small but significant resistance to malaria with
sickle cells.
48
Lack of globin chains: Example: thalassemia
– extravascular hemolysis. An inherited defect (autosomal codominant) that results in diminished or absent synthesis of either the alpha or beta globin chains of hemoglobin.
49
thalassemia: The cause at the gene level can include
whole or partial gene deletion, mutations in the coding sequence or promotor region, or mRNA instability.
50
The type of thalassemia is named for the
globin chain produced in reduced amounts.
51
Thalassemia: Decreased globin production results in .
decreased hemoglobin production, and anemia is the principal clinical manifestation.
52
Thalassemia: In addition, precipitation of the relative excess of the other globin chain within RBC causes
membrane damage and premature destruction of RBC precursors in the marrow and spleen (ineffective erythropoiesis and extravascular hemolysis).
53
Thalassemia: Clinical manifestations vary from
severe transfusion-dependent anemia and iron overload (thalassemia major) to mild anemia (thalassemia minor).
54
In almost all cases of Thalassemia, there is a moderate to marked
microcytosis (low MCV) with target cells and basophilic stippling of the red cells present on the blood smear.
55
Thalassemia: As the severity of the anemia increases there is increasing abnormalities of
red cell shapes and sizes.
56
Thalassemia is relatively common in persons of
Mediterranean, African, and Southeast Asian descent.
57
Thalassemia reduces the impact of
malaria
58
Metabolic defect: Example: Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency –
extravascular hemolysis. An inherited defect (X-linked) encountered primarily in blacks in which red cells are susceptible to oxidant injury by drugs or toxins (antimalarials, sulfonamides, etc.).
59
G6PD def.: The denaturation of oxidized hemoglobin causes it to
precipitate within the cell and attach to the RBC membrane.
60
G6PD def: The RBC membrane's flexibility is
reduced, leading to extravascular hemolysis.
61
G6PD def: The condition is asymptomatic in the absence of the
oxidant.
62
G6PD def: Red cell membrane is
less flexible and subjected to extravascular hemolysis in the spleen.
63
G6PD def: “Bite” cells:
cytomorphologic hallmark
| In the absence of “trigger”, individuals are asymptomatic
64
Immune destruction: Example: Erythroblastosis fetalis –
extravascular hemolysis. This disorder, also called hemolytic disease of the newborn (HDN), is caused by blood group incompatibility between the mother and fetus.
65
Erythroblastosis fetalis: This disease occurs in
utero only when the fetal RBC express antigens inherited from the father that are not present in the mother. Fetal RBC that reach the maternal circulation during the third trimester of pregnancy or during childbirth can be recognized as foreign and stimulate an antibody response in the mother.
66
Erythroblastosis fetalis: When a sensitized mother is re-exposed to the foreign antigen during a
subsequent pregnancy, the mother's immune system makes antibodies (IgG) that cross the placenta and attach to the fetal RBC, resulting in extravascular hemolysis (antibody coated RBC are removed from circulation in liver and spleen) in the fetus.
67
Erythroblastosis fetalis: most important antigens;
ABO and Rh antigens (especially anti-D) are most important in this disorder.
68
Rh-negative mothers are given
anti-D (Rhogam) within 72 hours of delivery of an Rh-positive fetus.
69
anti-D binds to the
Rh-positive fetal cells and removes them from the maternal circulation before the mother can generate an antibody response and become sensitized.
70
ABO hemolytic disease occurs in
group A and B infants born to group O mothers.
71
Certain group O mothers produce
IgG anti-A or anti-B in addition to the usual IgM antibodies (which do not cross the placenta).
72
fetal cells express A and B antigens
weakly, and other tissues also express A and B antigens and soak up the antibody.
73
ABO and Rh antigens are the
most common.
74
anti-D is given to group O negative mothers
routinely.
75
A and B infants of group O mothers are also
at risk
76
Example: Hemolytic transfusion reaction –
intravascular hemolysis. Here transfusion of incompatible red cells into a sensitized patient results in binding of antibody (in patient) to antigen (transfused RBC) with activation of complement (lyses antibody-coated RBC) and immediate intravascular hemolysis. Activation of coagulation cascade with bleeding, renal failure, shock, and death can occur.
77
Hemolytic transfusion: most important antigens:
ABO antigens are most important, but other RBC antigens can produce a similar picture.
78
Example: Autoimmune hemolysis –
extravascular hemolysis. Patient makes antibodies to his/her own RBCs. Antibody-coated cells can be lysed (complement activation) or removed by the reticuloendothelial system. Phagocytosis of antibody-coated RBC can lead to partial loss of red cell membrane (spherocytes). Spherocytes are sequestered by the spleen, further contributing to the anemia.
79
Mechanical trauma: Example: Cardiac valve prosthesis –
intravascular hemolysis. Red cells are disrupted by physical trauma as they pass through areas of turbulence and abnormal pressure related to abnormal valve function. Example: DIC (disseminated intravascular coagulation) where RBCs are lysed as they pass through fibrin clots/strands in the microcirculation.
80
Cardiac Valve Prosthesis: Loss of large portion of membrane produces
schistocytes.
81
Infections: Example: Malaria – .
intravascular hemolysis. Parasites infect RBC and cause lysis of RBC during maturation. Varying degrees of intravascular hemolysis are experienced by individual patients
82
• Iron Deficiency Anemia: Iron deficiency is the most common cause of
anemia worldwide. Iron is needed for hemoglobin, myoglobin, and a variety of enyzmes.
83
Iron deficiency: Red blood cells become
smaller (microcytic) and contain less hemoglobin (hypochromic) than usual.
84
Iron deficiency anemia occurs most commonly in
infants (inadequate intake), adolescents (increased requirement), pregnancy, elderly, and alcoholics.
85
It is important to recognize that iron deficiency anemia may also be a sign of a more serious disorder associated with
chronic blood loss (cancer).
86
Anemia develops
insidiously, and remarkably low levels of hemoglobin can be tolerated with minimal symptoms.
87
Iron deficiency anemia: Diagnosis is usually established by
laboratory tests (Microcytic (low MCV) red cells, Hypochromic (low MCHC) red cells, Decreased serum ferritin, Increased serum iron-binding capacity,Decreased serum iron,Absent reticulocyte response)
88
Vitamin B12 and Folate Deficiency (Megaloblastic anemia): Both B12 and folate are
involved either directly or as cofactors in the synthesis of thymidine, one of the purine bases in DNA.
89
B12 and folate deficiency: The impaired DNA synthesis causes a
delay in mitotic division: nuclear size increases, but RNA synthesis and cytoplasmic maturation proceed normally.
90
B12 and folate deficiency: The end result is an
abnormally large red cell precursor (megaloblast), decreased production of mature RBCs, and abnormally large red cells (macrocytes – high MCV).
91
B12 and folate deficiency: Hypersegmented neutrophils may
be seen secondary to the delay in mitotic division.
92
B12 and folate deficiency: The megaloblasts accumulate in the
bone marrow, releasing too few RBCs into the peripheral blood and causing anemia.
93
B12 and folate deficiency: The megaloblasts may undergo
autohemolysis in the marrow or be destroyed by phagocytic cells in the marrow (ineffective erythropoiesis).
94
B12 and folate deficiency: The impairment of DNA synthesis is
systemic, and affects other rapidly dividing cells in the body (granulocytes, megakaryocytes, epithelial cells).
95
Vitamin B12 is found in animal foods; deficiency can result from
decreased intake (strict vegans without vitamin supplementation), or malabsorption (lack of intrinsic factor, intestinal disease).
96
Patients with pernicious anemia have
autoantibodies directed against intrinsic factor.
97
A deficiency of B12 also causes a
demyelinating disorder.
98
Absorption of Vitamin B12 requires
intrinsic factor (IF), a protein produced by parietal cells of the gastric mucosa.
99
The IF-B12 complex passes to the ----------where it attaches to receptors on --------- and is absorbed.
distal ileum, epithelial cells
100
The absorbed B12 is bound to
transcobalamins (transport protein) in plasma which deliver it to the liver and other cells via the bloodstream.
101
Folate is found in
fresh vegetables; deficiency can result from increased requirements (pregnancy, hemolytic anemia), decreased dietary intake (alcoholics), and malabsorption (intestinal disease, drugs).
102
body stores of folate are
relatively small.
103
Folate is absorbed in the
proximal small intestine.
104
Since the megaloblastic features are indistinguishable morphologically in folate and B12 deficiencies, diagnosis is established by
laboratory tests (serum B12 level, serum and RBC folate levels, presence of antibodies directed against intrinsic factor);
105
Folate/b12 deficiency: treatment involves
replenishing body stores and defining how the anemia developed.
106
Aplastic Anemia: Production of all cellular elements of the blood (red cells, white cells, and platelets) is
markedly decreased (pancytopenia).
107
Aplastic anemia: Over half of the cases have no known
predisposing cause (idiopathic), but viruses (hepatitis), drugs (chloramphenicol) and toxins (benzene, radiation) have been implicated.
108
Aplastic anemia: Two major pathogenetic theories exist:
1. an acquired defect in stem cell production or 2. asuppression of stem cells by T lymphocytes.
109
Aplastic anemia must be distinguished from other causes of
marrow failure.
110
Aplastic anemia: Clinical problems result from
anemia (weakness, fatigue), leukopenia (infections), and decreased platelets (bleeding).
111
Aplastic anemia: ---------------- has been successful, especially in patients less than 40 years old.
Bone marrow transplantation
112
Myelophthisic Anemia
Decreased production of red cells due to replacement of marrow elements
----The normal hematopoietic cells in the marrow are crowded out by tumor (usually multiple myeloma or metastatic cancer) or fibrosis.
113
The opposite of anemia is
polycythemia, an increase in red cell mass.
114
Relative polycythemia occurs with
hemoconcentration from dehydration, vomiting, diarrhea, or excessive use of diuretics.
115
Absolute polycythemia can be a
primary or secondary phenomenon.
116
Stimuli which increase erythropoietin (a growth and differentiation factor for red cell precursors) can produce
secondary absolute polycythemia (these include cyanotic heart disease, pulmonary disease, living at high altitude, abnormal hemoglobin, erythropoietin-producing tumor).
117
Primary absolute polycythemia occurs when a
non-regulated (neoplastic) proliferation of red cells and myeloid cells is called polycythemia vera. This condition is a stem cell disorder and is associated with normal or low levels of erythropoietin.
118
Polycythemia vera can cause
neurologic and visual abnormalities due to sludging of red cells in capillaries.
119
polycythemia vera: Treatment is removal of
excess RBC by phlebotomy.
120
---------------- are helpful in distinguishing primary from secondary cases of absolute polycythemia.
Erythropoietin levels
121
Cases of secondary absolute polycythemia have increased levels of
erythropoietin
122
primary absolute polycythemia has
normal or suppressed levels of erythropoietin.
