MLT GlobeHematology: Hemolytic anemias & hemoglobinopathies
120 Hematology MCQs on Hemolytic anemias & hemoglobinopathies with answers and explanations.
How many heme groups does one molecule of adult hemoglobin contain, and so how many O2 molecules can it bind?
Hemoglobin is a tetramer of four globin chains, each carrying one heme with ferrous iron, so one molecule binds up to four O2 molecules.
Which hemoglobin makes up about 95–98% of total hemoglobin in a healthy adult?
HbA (α2β2) predominates in adults, with small amounts of HbA2 (<3.5%) and HbF (<1%). HbS and HbC are abnormal variants.
Which inherited anemia is caused by reduced globin chain synthesis rather than a red cell membrane defect?
Thalassemias are quantitative globin disorders. Spherocytosis, elliptocytosis and stomatocytosis stem from defects in membrane or cytoskeletal proteins or membrane permeability.
A child with microcytic anemia and normal ferritin is suspected of β-thalassemia. Which test confirms the diagnosis?
HPLC or electrophoresis shows raised HbA2 and HbF typical of β-thalassemia. A CBC suggests the diagnosis but cannot confirm it.
A boy develops acute hemolysis with bite cells after eating fava beans. Which enzyme deficiency is most likely?
G6PD deficiency leaves red cells unable to generate NADPH, so oxidants in fava beans cause hemolysis (favism). It also causes neonatal jaundice.
Normal adult HbA is made of which globin chain pair?
HbA is α2β2. α2δ2 is HbA2, α2γ2 is HbF and epsilon chains occur in embryonic hemoglobins.
How many β-globin chains does fetal hemoglobin (HbF) contain?
HbF is α2γ2, with gamma chains in place of beta chains. This is why β-thalassemia and sickle cell disease are silent before birth.
The disorder described by Thomas Cooley, presenting in infancy with severe transfusion-dependent anemia and bone changes, is:
Cooley's anemia is homozygous or compound heterozygous β-thalassemia with severe ineffective erythropoiesis, marrow expansion and lifelong transfusion need.
Which hemoglobin pattern is expected in a healthy adult?
Adults have over 95% HbA, HbA2 below about 3.5% and HbF below 1–2%. High HbF is normal at birth; 40% HbS indicates sickle cell trait.
Hemoglobin HPLC in homozygous sickle cell disease shows predominantly:
In HbSS there is no HbA; HbS makes up most hemoglobin with variable HbF and normal HbA2. HbH (β4) belongs to α-thalassemia.
The sickle cell mutation replaces which amino acid at position 6 of the beta-globin chain?
HbS results from glutamic acid → valine at beta-6. Glutamic acid → lysine at the same position gives HbC. The hydrophobic valine makes deoxygenated HbS polymerise and sickle the cell.
A man develops hemolysis after taking primaquine. A supravital stain shows Heinz bodies and the smear shows 'bite' cells. The most likely cause is:
G6PD-deficient cells cannot make enough NADPH to protect hemoglobin from oxidation. Oxidant drugs or fava beans denature hemoglobin into Heinz bodies, which the spleen 'bites' out.
Hereditary elliptocytosis is most commonly caused by a defect in:
Most hereditary elliptocytosis is due to alpha- or beta-spectrin mutations that weaken horizontal skeleton interactions, so cells cannot recover their shape. Band 3 defects cause spherocytosis or ovalocytosis instead.
The main role of glucose-6-phosphate dehydrogenase (G6PD) in red cells is to:
G6PD is the first enzyme of the hexose monophosphate shunt and generates NADPH, which keeps glutathione reduced to protect hemoglobin from oxidants. ATP comes from the Embden-Meyerhof pathway, not the shunt.
G6PD deficiency is inherited as which pattern?
The G6PD gene lies on the X chromosome, so males are usually affected and females are carriers, although some heterozygous females are affected due to lyonization. Pyruvate kinase deficiency, not G6PD deficiency, is autosomal recessive.
In paroxysmal nocturnal hemoglobinuria, red cells are sensitive to complement because they lack:
An acquired PIGA mutation prevents GPI-anchor synthesis, so the GPI-linked complement regulators CD55 (DAF) and CD59 (MIRL) are missing. CD34 and CD38 are stem cell and maturation markers unrelated to complement control.
Which plasma test result is typically DECREASED in intravascular hemolysis?
Haptoglobin binds free hemoglobin and the complex is rapidly cleared by the liver, so the level falls. LDH, unconjugated bilirubin and free hemoglobin all rise in hemolysis.
A 4-year-old develops acute kidney injury, thrombocytopenia and schistocytes one week after bloody diarrhea. The most likely cause is:
Typical hemolytic uremic syndrome follows infection with Shiga toxin-producing E. coli such as O157:H7, with toxin damaging renal endothelium. C. difficile causes colitis but not classic HUS.
In the sickle cell solubility test, a positive result appears as turbidity because:
Sodium dithionite deoxygenates hemoglobin, and deoxy-HbS polymerizes and is insoluble in concentrated phosphate buffer, making the solution cloudy. Saponin only lyses the cells; it does not agglutinate them.
On cellulose acetate electrophoresis at alkaline pH (8.4–8.6), HbC migrates in the same position as:
At alkaline pH, HbC is the slowest common hemoglobin and co-migrates with HbA2, HbE and HbO-Arab. HbD and HbG co-migrate with HbS, not with HbC.