MLPAO Hematology and Coagulation Advanced Practice 2 — Questions and Answers
Question 1: What is the significance of finding teardrop cells (dacrocytes) on a peripheral blood smear?
- Iron deficiency anemia
- Myelofibrosis or bone marrow infiltration (Correct answer)
- Sickle cell disease
- Liver cirrhosis
Correct answer: Myelofibrosis or bone marrow infiltration
Teardrop cells (dacrocytes) are characteristic of myelofibrosis and conditions causing marrow infiltration (myelophthisis). They form as red blood cells are forced through fibrotic bone marrow tissue. The presence of teardrop cells with nucleated red blood cells and immature granulocytes (leukoerythroblastic picture) strongly suggests marrow pathology.
Question 2: Which hemoglobin variant migrates in the same position as HbS on alkaline electrophoresis?
- HbC
- HbD and HbG (Correct answer)
- HbE
- HbH
Correct answer: HbD and HbG
HbD and HbG migrate in the same position as HbS on alkaline (cellulose acetate) electrophoresis at pH 8.6. To differentiate these variants, a second method such as acid electrophoresis (citrate agar at pH 6.2) or HPLC is required, as they separate differently under acidic conditions.
Question 3: What is the mechanism of action of warfarin?
- Direct thrombin inhibition
- Inhibition of vitamin K epoxide reductase, reducing functional vitamin K-dependent factor synthesis (Correct answer)
- Enhancement of antithrombin activity
- Irreversible platelet COX-1 inhibition
Correct answer: Inhibition of vitamin K epoxide reductase, reducing functional vitamin K-dependent factor synthesis
Warfarin inhibits vitamin K epoxide reductase (VKORC1), blocking the recycling of vitamin K to its active reduced form. This impairs the gamma-carboxylation of vitamin K-dependent coagulation factors (II, VII, IX, X) and proteins C and S, reducing their functional activity.
Question 4: Which laboratory finding differentiates thrombotic thrombocytopenic purpura (TTP) from hemolytic uremic syndrome (HUS)?
- TTP has schistocytes; HUS does not
- TTP has severely decreased ADAMTS13 activity; HUS typically does not (Correct answer)
- TTP has elevated fibrinogen; HUS has decreased fibrinogen
- TTP affects only children; HUS affects only adults
Correct answer: TTP has severely decreased ADAMTS13 activity; HUS typically does not
TTP is characterized by severely deficient ADAMTS13 activity (<10%), the metalloprotease that cleaves von Willebrand factor multimers. In typical HUS (caused by Shiga toxin-producing E. coli), ADAMTS13 activity is normal. Both conditions show thrombocytopenia, MAHA with schistocytes, and organ damage.
Question 5: What is the principle of the thrombin time (TT) test?
- Measures the time for plasma to clot after adding tissue factor
- Measures the time for plasma to clot after adding thrombin directly (Correct answer)
- Measures platelet adhesion to collagen
- Measures the activity of Factor VIII
Correct answer: Measures the time for plasma to clot after adding thrombin directly
The thrombin time measures the time for fibrin clot formation after adding exogenous thrombin directly to citrated plasma, bypassing the intrinsic and extrinsic pathways. It evaluates the final step of coagulation (fibrinogen to fibrin conversion) and is prolonged by heparin, low fibrinogen, dysfibrinogenemia, and elevated FDPs.
Question 6: Which condition is associated with basophilic stippling of red blood cells?
- Iron deficiency anemia
- Lead poisoning and thalassemia (Correct answer)
- Hereditary spherocytosis
- Paroxysmal nocturnal hemoglobinuria
Correct answer: Lead poisoning and thalassemia
Basophilic stippling (blue granules in red blood cells representing aggregated ribosomes) is characteristically seen in lead poisoning (lead inhibits pyrimidine 5'-nucleotidase) and thalassemia. It can also be seen in sideroblastic anemia, heavy metal poisoning, and myelodysplastic syndromes.
MLPAO Hematology and Coagulation Advanced Practice 2
What is the significance of finding teardrop cells (dacrocytes) on a peripheral blood smear?