Red Cell Disorders Flashcards
Blood cellular elements
Peripheral blood film (smear)
Bone marrow aspirate
Bone marrow biopsy (tissue section)
Automated complete blood counts (CBC)
Red cell part
White cell part
Platelet part
CBC: red cells
Hemoglobin concentration -Measured spectrophotometrically (HiCN) Hematocrit -Fraction of whole blood that is red cells RBC concentration (RBC count) -Measured directly by particle counting -Impedance and/or electro-optical methods Red cell indices
Red cell indicies
MCV (mean cell volume)
-Average volume per red cell
-Measured by impedance and/or electro-optically
MCH (mean cell hemoglobin)
-Average content (mass) of hemoglobin per red cell
MCHC (mean cell hemoglobin concentration)
-Average concentration of hemoglobin in the red cells
RDW (red cell distribution width)
-Coefficient of variation of red cell volume
CBC: Red cells
Hemoglobin (g/dl): measured Hematocrit (%): calculated (MCV x RBC) RBC count (x106/µl): measured MCV (fl): measured MCH (pg): calculated (Hgb/RBC) MCHC (g/dl): calculated (Hgb/Hct) RDW (%): measured (SD/MCV)
CBC: White cells
WBC count (x103/µl) Differential count [5 part] (% of total WBC) Absolute counts (cells/µl) Lymphocytes Monocytes Neutrophils Eosinophils Basophils
CBC: platelets
Platelet count (x103/µl)
MPV (mean platelet volume) (fl)
PDW (platelet distribution width) (%)
Reticulocyte Count
Manual
-Number of Reticulocytes per 100 red cells
Automated
-% Retics
*Normal: 0.5-1.5%
*% counts must be corrected for degree of anemia
-Absolute count
*Normal: 24,000-84,000/µl
3% or 150,000/µl is a useful guide for a good marrow response to moderate anemia
Red Cells on Blood Films
Evaluate the size, color, and shape of the red cells
Assess by
-Direct examination of blood film (smear)
-Red cell indices
Correlates with cause of anemia
Helps in choosing logical next steps
Size: Microcytic, normocytic, or macrocytic
Color: Hypochromic or normochromic
Shape: Normal or a variety of possible abnormal forms
Size & color
Normochromic normocytic Polychromasia Hypochromic, microcytic Macrocytic
Shape
Spherocytes Eliptocytes Target cells Schistocytes Poikilocytosis
Hemoglobin
Tetramer of globin chains
Each chain has a heme prosthetic group capable of binding oxygen
Heme is a porphyrin ring and a coordinated iron atom
Adult blood contains 3 hemoglobins
HbA, α2β2, 97% of total
HbF, α2γ2, 3-5%
HbA2, α2δ2, 1.5-3.5%
Normal and variant hemoglobins can be detected and quantified by electrophoresis, HPLC, or isoelectric focusing
Red cell disorders typically manifest as
Anemia
-Decreased number of red cells
Polycythemia
-Increased number of red cells
Anemia
Reduction of oxygen carrying capacity of blood
-Reduction of red cell mass
-Labs
Decreased hemoglobin concentration (Hgb)
Decreased hematocrit (Hct)
Decreased red cell concentration (RBC count)
Response to Anemia
Decreased tissue oxygen tension →
Increased erythropoietin production →
Hyperplasia of erythroid precursors
-May even lead to extramedullary hematopoiesis
Reticulocytosis is the hallmark of increased marrow output of red cells
Anemia clinical
Clinical consequences depend upon severity, speed of onset, and mechanism
Pallor, fatigue, and lassitude are common presenting symptoms
Slow onset gives more time to adapt
Premature destruction
-Hyperbilirubinemia, jaundice, pigment gallstones
Ineffective erythropoiesis
-Increased iron absorption, iron overload
Severe congenital anemias
-Growth retardation, skeletal abnormalities, cachexia
Anemia of Blood Loss
Acute blood loss
chronic blood loss
Acute blood loss
Hypovolemia is the most immediate threat
-Cardiovascular collapse, shock, and death
Fluid volume is fully restored in 2-3 days
-Hemodilution reveals the extent of the anemia
-Normochromic, normocytic anemia
Red cell production increases in several days
-↑ Epo → Erythroid precursors → Red cells
Chronic blood loss
Anemia develops when
Rate of blood loss exceeds production capacity
Run out of raw material, e.g. iron
Hemolytic anemias
Anemias associated with accelerated destruction of red cells
Classify by cause
Intrinsic, or intracorpuscular, factors
-Most inherited
*Membrane abnormalities, enzyme deficiencies, hemoglobin synthesis disorders
Extrinsic, or extracorpuscular, factors
-Acquired
*Immune mediated, mechanical destruction, infections
Hemolytic Anemias general features
Shortened red cell life span
-Premature red cell destruction
Increased rate of erythropoiesis
-Reticulocytosis
Accumulation of the products of hemoglobin catabolism
-Iron accumulation is a problem in chronic hemolytic anemias
*Iron is recycled and gut absorption is increased
Hemolytic Anemias
Extravascular hemolysis
Intravascular hemolysis
Extravascular hemolysis
Red cell destruction within the cells of the mononuclear phagocyte system
-More common mode of red cell destruction
Occurs largely within the spleen and liver
Removes damaged and immunologically targeted red cells from the circulation
Leads to
-Jaundice
-Pigment gallstones
-Haptoglobin decrease
-Reactive hyperplasia of the mononuclear phagocyte system i.e., splenomegaly
Intravascular hemolysis
Red cell destruction within the vascular space
-Less common mode
Results from
-Mechanical damage
*Defective heart valve
-Biochemical or chemical damage to the membrane
*Complement fixation, clostridial toxins, or heat
Leads to:
Hemoglobinemia
Hemoglobinuria
Hemosiderinuria
Unconjugated hyperbilirubinemia
Jaundice
Haptoglobin absence from plasma
Acute tubular necrosis in kidney, if massive hemolysis
Hereditary Spherocytosis
Inherited defect in the red cell membrane that renders the red cells spheroidal, less deformable, and vulnerable to splenic sequestration and destruction
Autosomal dominant, most common
Autosomal recessive 25% of the time, more severe form
Hereditary Spherocytosis
defect
Defect is in the membrane cytoskeleton that stabilizes the red cell membrane
-Ankyrin most common defective protein
-Band 3 next most common
-Spectrin (α and β) and band 4.2 most of remainder
Reduced membrane stability → loss of membrane fragments (but retain volume) after release into the periphery → become spherical
Spherical cells are have limited deformability → sequestered in splenic cords → destroyed by macrophages
Spleen is critical element in causing the anemia
Hereditary Spherocytosis
features
Splenomegaly, 500-1000 g Spherocytes in peripheral blood Note: Not all spherocytes are HS !! Reticulocytosis Erythroid hyperplasia of marrow Hemosiderosis Jaundice, mild Pigment gallstones, 30-40% of adults
Hereditary Spherocytosis clinical
Anemia -Most moderate varies from subclinical to profound *20-30% virtually asymptomatic Splenomegaly Jaundice Generally stable Punctuated sometimes by -Aplastic crisis *Parvovirus B19 infection Hemolytic crisis -Increased splenic sequestration and destruction -Usually associated with an intercurrent event like infectious mononucleosis Gallstones
Hereditary Spherocytosis Diagnosis
Family history, hematological findings, and laboratory evidence
- Osmotic fragility test
- Increased red cell lysis when incubated in hypotonic saline (in about 2/3 of cases)
- MCHC increased
Hereditary Spherocytosis treatment
No specific treatment
Splenectomy can correct the anemia but not the spherocytosis
G6PD Deficiency epidemiology
X-linked recessive Glucose-6-phosphate dehydrogenase deficiency -G6PD A- variant -10% of black Americans Protective against Plasmodium falciparum
G6PD Deficiency path
Intravascular hemolysis predominantly
-Mild component of extravascular
Decreased NADPH and glutathione
-GSH neutralizes peroxide and other reactive oxygen species
-Oxidized hemoglobin → precipitates as Heinz bodies
*Heinz bodies damage red cell membrane → hemolysis
*Heinz bodies are removed by splenic macrophages → bite cells
G6PD A-
Moderately reduced half-life
Episodic hemolysis after exposure to oxidative stress
Oxidative stresses
Infection—most common
Drugs
-Primaquine, chloroquine, sulfonamides
G6PD Deficiency
clinical
Sudden onset of back pain with hemoglobinuria 2 to 3 days after an oxidant stress
Hemolysis is self-limited
G6PD Deficiency
labs
Normocytic anemia Heinz bodies -Best seen during active hemolysis -Supravital staining Bite cells RBC enzyme analysis -After hemolysis has subsided
Sickle Cell Disease epidemiology
Autosomal recessive Most common hemoglobinopathy in black Americans Heterozygous (Sickle cell trait, HbAS) -No anemia -8% of black Americans Homozygous (Sickle cell disease, HbSS) -Anemia Protective against falciparum malaria
Sickle Cell Disease path
Missense point mutation in β-globin gene
-Glutamic acid to valine at 6th position of β chain
HbS aggregates and polymerizes when deoxygenated
-Causes red cells to change shape (sickle or boat shape)
-Sickling is reversible initially with reoxygenation
-Repeated sickling leads to membrane damage and eventually to irreversible sickling
-Membrane damage leads to intracellular dehydration
-Sickling makes the cells “sticky”
Extravascular hemolysis predominantly of sickle cells
Factors that affect rate and degree of sickling
Amount of HbS
-HbS in HbAS is too low to produce sickling or anemia
Interaction with other hemoglobins
-HbS interacts weakly with HbA
-HbF inhibits HbS polymerization
*Infants are usually 6 months old before disease manifests
-HbC (HbSC Disease) milder disease than HbSS
*2-3% of black Americans heterozygous for HbC
Factors that affect rate and degree of sickling contin
MCHC -↑ MCHC → more sickling (membrane damage) -↓ MCHC → less sickling (α-thalassemia) Acidosis → more sickling Time in low oxygen tension -Normal capillary flow → no sickling -Sluggish flow → more sickling *Spleen, bone marrow -Inflammation → more sickling -Stickiness → more sickling
Sickle Cell Disease clinical
Key processes are chronic hemolysis and tissue injury from vascular occlusion
-Extravascular hemolysis
*Irreversibly sickled cells are recognized and removed by the mononuclear phagocytes
*Minor intravascular hemolysis results from the mechanical fragility of sickled cells
Microvascular occlusion results primarily from increased adhesiveness and inflammation
Sickle Cell Disease Crisis
Vaso-occlusive crises (pain crises)
Sequestration crisis
Aplastic crisis
Vaso-occlusive crises (pain crises)
Episodes of hypoxic tissue injury and infarction associated with severe pain
Sequestration crisis
Rapid enlargement of spleen with entrapment of red cells can result in hypovolemic shock
Aplastic crisis
Transient cessation of erythropoiesis
Parvovirus B19
↓ Reticulocytes, worsening anemia
Autosplenectomy
Spleen is enlarged but dysfunctional by age 2
-Howell-Jolly bodies appear
Chronic erythrostasis causes hypoxic tissue damage and fibrosis
Spleen becomes a small piece of fibrous tissue
Increased susceptibility to infections
Encapsulated bacteria
-Pneumococcus, H flu
-Sepsis and meningitis are most common cause of death in children
Salmonella osteomyelitis
Sickle cell disease
Acute chest syndrome -Vaso-occlusion of pulmonary capillaries -Most common cause of death in adults Dactylitis -Painful swelling of hands and feet in infants (6-9 mo) -Due to bone infarcts Stroke / Seizures Aseptic necrosis of femoral head Leg ulcers Calcium bilirubinate gallstones Renal findings in HbAS and HbSS -Microhematuria due to medulla infarcts -Lose concentrating ability
Sickle Cell Disease Lab
Sickle cell screen -Sodium metabisulfite reduces O2 tension, induces sickling Hb electrophoresis -HbAS: HbA 55-60%, HbS 40-45% -HbSS: HbS 90-95%, HbF 5-10%, no HbA Peripheral Blood -HbAS: normal -HbSS: sickle cells, target cells Prenatal screening -Fetal DNA to detect point mutation
Sickle Cell Disease treatment
hydroxyurea “Gentle” inhibitor of DNA synthesis ↑ HbF ↓ Leukocytes → anti-inflammatory ↑ MCV → ↓ MCHC Nitrous oxide (NO) production -Vasodilation -Inhibits platelet aggregation
Thalassemias
A heterogeneous group of disorders characterized by diminished globin synthesis
Epidemiology
-Autosomal recessive
-α-thalassemia in Southeast Asia, black Americans
-β-thalassemia in black Americans, Greeks, Italians
α-Thalassemia path
Decreased α-globin chain synthesis due to gene deletions -4 genes for α-globin -Lie in tandem on chromosome 16 Silent carrier: -One gene deletion Asymptomatic, normal red cells
α-thalassemia trait
Two gene deletion Mild anemia, increased RBC count Black American type (α - / α - ) Asian type (- - / α α) -At risk for more severe types in offspring Labs -Decreased MCV, Hb, Hct -Increased RBC count -Normal RDW, serum ferritin, Hb electrophoresis No treatment required
HbH (β4) disease
Three gene deletion
Moderately severe hemolytic anemia
-HbH is a mildly unstable hemoglobin with high oxygen affinity
-Excess β chains form inclusions that are removed by macrophages and result in the destruction of the red cells
*Also has some effect on erythroid precursors but erythropoiesis is effective
-Average Hgb is 3 g/dl less than normal controls
HbH on electrophoresis (5-30%)
Hb Bart (γ4) disease
Four gene deletion
Hb Bart is a high affinity hemoglobin useless for oxygen delivery to the tissues
Intrauterine death
-Intrauterine transfusion is possible and can save some
Hb Bart on electrophoresis (>80%)
-HbH and Hb Portland
β-Thalassemia path
Mutations in β globin gene -Promoter region -Coding sequence -Splice sites Results in either -β0 No chain synthesis -β+ Diminished chain synthesis
β-thalassemia minor (β/β+) [β-thal trait]
Mild microcytic anemia or microcytosis without anemia
Mild protection against falciparum malaria
Shortened red cell life span
β-thalassemia minor (β/β+) [β-thal trait] labs
Decreased MCV, Hb, Hct Increased RBC count Normal RDW, serum ferritin Hb electrophoresis -Decreased HbA, Increased HbA2 and HbF
β-thalassemia major (β0/β0) [Cooley’s anemia]
Severe hemolytic anemia
Excess α chains precipitate
-Membrane damage and extravascular hemolysis
-Erythroid precursors undergo apoptosis (ineffective erythropoiesis)
Extramedullary hematopoiesis
β-thalassemia major (β0/β0) [Cooley’s anemia]
labs
Increased RDW, reticulocytes Hb electrophoresis: No HbA, Increased HbA2 and HbF Long term transfusion requirement -Systemic iron overload Bone marrow transplantation
β-Thalassemia other gene combos
Variable and intermediate disease
Depending on amount of β-globin produced
Paroxysmal Nocturnal Hemoglobinuria path
Acquired membrane defect in multipotential myeloid stem cells
-Red cells, granulocytes, and platelets affected
-Loss of GPI anchor that complement regulatory proteins use to attach to the red cell surface
*Decay accelerating factor, CD55
*Membrane inhibitor of reactive lysis, CD59
-Cells are more susceptible to complement lysis
Intravascular complement mediated lysis of red cells, neutrophils, and platelets
-Nocturnal because acidosis enhances complement attachment to cells
*Paroxysmal and nocturnal only 25% of the time
*Chronic hemolysis without dramatic hemoglobinuria is more common
Paroxysmal Nocturnal Hemoglobinuria clinical
Episodic hemoglobinuria
Increased incidence of thrombosis
Increased incidence of severe infections
Association with aplastic anemia
Paroxysmal Nocturnal Hemoglobinuria labs
Sucrose hemolysis test (sugar water test) -Screening test -Sugar enhances complement attachment Acidified serum test (Ham test) -Confirmatory test -Activates alternative complement pathway Peripheral Blood -Normocytic anemia with pancytopenia *Microcytic if iron deficiency develops
Immune Hemolytic Anemia
Extrinsic hemolytic anemias with extravascular or intravascular hemolysis Antibodies and/or complement play a central role Classification Autoimmune -Warm type -Cold type Drug induced Alloimmune
Warm Autoimmune Hemolytic Anemia
70% of AIHA
Primary (idiopathic) 50%
Secondary
-Leukemia, lymphoma, other neoplastic disease, autoimmune disease (esp. SLE)
Warm Autoimmune Hemolytic Anemia path
IgG antibodies that react against red cell antigens coat the red cells
IgG may fix C3b to the red cells
Extravascular hemolysis
-IgG and/or C3b coated red cells are phagocytosed by macrophages in the spleen and liver
Warm Autoimmune Hemolytic Anemia clinical & lab
Jaundice
Splenomegaly
Positive Direct Antiglobulin Test (DAT, Coombs’ test)
-Detects RBCs sensitized with IgG and/or C3b
Positive Indirect Antiglobulin Test (IAT, indirect Coombs’ test)
-Detects red cell reactive antibodies in the serum
Unconjugated hyperbilirubinemia
Peripheral blood
-Normocytic anemia, spherocytes may be present
Cold Autoimmune Hemolytic Anemia
30% of AIHA Primary (idiopathic) Secondary -Post-infection (mycoplasma, infectious mononucleosis) -Lymphoid neoplasms
Cold Autoimmune Hemolytic Anemia oath
IgM antibodies bind red cells usually in cooler areas of the body
IgM fixes complement to the red cell
IgM dissociates at warmer temperatures in most cases
May result in intravascular hemolysis if complement is activated through to the membrane attack complex
Otherwise, extravascular hemolysis
-C3b coated cells are phagocytosed by macrophages in the liver
Cold Autoimmune Hemolytic Anemia clinical labs
Hepatosplenomegaly
Raynaud’s phenomenon may result from IgM induced red cell agglutination in the cooler peripheral circulation
Positive DAT (for C3b) If intravascular hemolysis, -Hemoglobinuria -Hemoglobinemia -Decreased haptoglobin
Drug Induced Immune Hemolytic Anemia mechanisms
Drug absorption
Immune complex
Autoantibody
Membrane modification
Drug absorption
Penicillin
Drug absorbs onto red cells → Antibody binds drug on cell → extravascular hemolysis
Immune complex
Quinidine
Drug-Antibody complexes are absorbed onto the red cells → +/- complement fixation → intravascular or extravascular hemolysis
Autoantibody
α-methyldopa
Drug induces a red cell autoantibody
Indistinguishable from warm AIHA
Antibody usually disappears in several months, if drug is discontinued
Membrane modification
Cephalosporins
Red cells become “sticky”
Immunoglobulin and complement components adhere non-specifically
Angiopathic Hemolytic Anemia
Intravascular hemolysis due to vascular lesions causing direct mechanical damage to the red cells
Macroangiopathic
hemolytic anemia
Calcified stenotic aortic valve
-Sheer forces due to turbulent flow and abnormal pressure gradients
Artificial mechanical heart valves
Microangiopathic hemolytic anemia
Microvascular lesions such as fibrin or platelet thrombi damage red cells as they pass
- Disseminated intravascular coagulation (DIC)
- Most common cause of microangiopathic hemolytic anemia
- Thrombotic thrombocytopenic purpura (TTP)
- Hemolytic uremic syndrome (HUS)
- Malignant hypertension
- Systemic lupus erythematosus
- Disseminated cancer
Microangiopathic hemolytic anemia peripheral blood
Microangiopathic hemolysis is an important diagnostic clue rather than a major problem in and of itself
Peripheral Blood
-Red cell fragments (schistocytes)
*Helmet cells, triangle cells, burr cells
