ASCP Coagulation 2

Question 1

Which factor is the first to decrease to critically low levels during warfarin therapy due to its shortest half-life?

Accepted Answer

Factor VII

Answer

Factor VII has the shortest half-life (approximately 4–6 hours) among vitamin K-dependent factors II, VII, IX, and X. It decreases first during warfarin initiation, explaining the early PT prolongation before full anticoagulation is achieved.

Question 2

The Bethesda assay is used to quantify:

Accepted Answer

Factor VIII inhibitor titer

Answer

The Bethesda assay measures Factor VIII inhibitor (neutralizing antibody) titer in Bethesda units (BU). One BU is the amount of inhibitor that neutralizes 50% of Factor VIII activity in a normal plasma mixture.

Question 3

Lupus anticoagulant (LA) causes what pattern on mixing studies?

Accepted Answer

Prolongs the aPTT that does NOT correct on mixing study

Answer

Lupus anticoagulant prolongs phospholipid-dependent clotting tests (aPTT, dRVVT) in vitro, but does NOT correct when mixed with normal plasma because the antibody is still present in the diluted mixture — an inhibitor pattern.

Question 4

Protein C deficiency leads to thrombosis because protein C normally:

Accepted Answer

Inactivates Factors Va and VIIIa

Answer

Activated protein C (APC), with its cofactor protein S, proteolytically inactivates Factors Va and VIIIa, downregulating thrombin generation. Protein C deficiency removes this brake, causing hypercoagulability.

Question 5

A prolonged thrombin time (TT) with a normal reptilase time most likely indicates:

Accepted Answer

Heparin contamination

Answer

Thrombin is inhibited by heparin via antithrombin, prolonging TT. Reptilase (ancrod) is not inhibited by heparin or antithrombin, so reptilase time is normal with heparin. Both TT and reptilase time are prolonged in fibrinogen deficiency and dysfibrinogenemia.

ASCP Practice Test

ASCP Practice Test

ASCP Coagulation 2