MLPAO Hematology and Coagulation Advanced Practice 2

Question 1

What is the significance of finding teardrop cells (dacrocytes) on a peripheral blood smear?

Accepted Answer

Myelofibrosis or bone marrow infiltration

Answer

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?

Accepted Answer

HbD and HbG

Answer

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?

Accepted Answer

Inhibition of vitamin K epoxide reductase, reducing functional vitamin K-dependent factor synthesis

Answer

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)?

Accepted Answer

TTP has severely decreased ADAMTS13 activity; HUS typically does not

Answer

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?

Accepted Answer

Measures the time for plasma to clot after adding thrombin directly

Answer

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.

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO - Medical Laboratory Professionals Association of Ontario Practice Test

MLPAO Hematology and Coagulation Advanced Practice 2