AACC Hematology & Coagulation 2

Question 1

Which coagulation factor is deficient in classic Hemophilia A?

Accepted Answer

Factor VIII

Answer

Hemophilia A is caused by a deficiency of Factor VIII, an essential cofactor in the intrinsic coagulation pathway, resulting in prolonged aPTT.

Question 2

The prothrombin time (PT) primarily evaluates which coagulation pathway?

Accepted Answer

Extrinsic and common pathways

Answer

PT measures the extrinsic and common pathways (Factors VII, X, V, II, and fibrinogen) and is initiated by tissue factor (thromboplastin) added to the sample.

Question 3

Which laboratory test is the standard for monitoring unfractionated heparin (UFH) therapy?

Accepted Answer

Activated partial thromboplastin time (aPTT)

Answer

UFH is monitored with aPTT because heparin potentiates antithrombin III inhibition of intrinsic pathway factors, prolonging the aPTT; therapeutic range is typically 1.5–2.5× control.

Question 4

What is the mechanism of action of warfarin as an anticoagulant?

Accepted Answer

Inhibition of vitamin K–dependent carboxylation of Factors II, VII, IX, and X

Answer

Warfarin inhibits vitamin K epoxide reductase, preventing the recycling of vitamin K needed for carboxylation and activation of Factors II, VII, IX, X, and proteins C and S.

Question 5

A patient presents with prolonged bleeding time, normal PT, and normal aPTT. Which condition is most likely?

Accepted Answer

Von Willebrand disease or platelet dysfunction

Answer

Isolated prolonged bleeding time with normal PT and aPTT indicates a defect in primary hemostasis, most commonly von Willebrand disease or platelet function disorders.

AACC - American Association for Clinical Chemistry Certification Practice Test

AACC - American Association for Clinical Chemistry Certification Practice Test

AACC Hematology & Coagulation 2