AACC Hematology & Coagulation 2 — Questions and Answers
Question 1: Which coagulation factor is deficient in classic Hemophilia A?
- Factor IX
- Factor VII
- Factor VIII (Correct answer)
- Factor XI
Correct answer: Factor VIII
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?
- Intrinsic pathway only
- Extrinsic and common pathways (Correct answer)
- Intrinsic and common pathways
- Fibrinolytic pathway
Correct answer: Extrinsic and common pathways
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?
- Prothrombin time (PT)
- Activated partial thromboplastin time (aPTT) (Correct answer)
- Thrombin time (TT)
- Anti-Xa activity assay
Correct answer: Activated partial thromboplastin time (aPTT)
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?
- Direct inhibition of thrombin (Factor IIa)
- Inhibition of vitamin K–dependent carboxylation of Factors II, VII, IX, and X (Correct answer)
- Binding to antithrombin III to inhibit Factor Xa
- Blocking platelet ADP receptors to prevent aggregation
Correct answer: Inhibition of vitamin K–dependent carboxylation of Factors II, VII, IX, and X
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?
- Hemophilia A
- Vitamin K deficiency
- Von Willebrand disease or platelet dysfunction (Correct answer)
- Factor V Leiden mutation
Correct answer: Von Willebrand disease or platelet dysfunction
Isolated prolonged bleeding time with normal PT and aPTT indicates a defect in primary hemostasis, most commonly von Willebrand disease or platelet function disorders.
Question 6: Which coagulation pathway is initiated by the exposure of tissue factor (thromboplastin) to blood?
- Intrinsic pathway
- Common pathway
- Fibrinolytic pathway
- Extrinsic pathway (Correct answer)
Correct answer: Extrinsic pathway
The extrinsic pathway is triggered when tissue factor (released from damaged subendothelial cells) binds Factor VIIa to activate Factor X, initiating coagulation.
Question 7: What is the role of fibrinogen (Factor I) in secondary hemostasis?
- Activating Factor XIII to crosslink fibrin
- Serving as the substrate for thrombin to generate fibrin clot (Correct answer)
- Inhibiting plasminogen to prevent premature fibrinolysis
- Chelating calcium to stabilize clot formation
Correct answer: Serving as the substrate for thrombin to generate fibrin clot
Thrombin (Factor IIa) cleaves fibrinogen into fibrin monomers that polymerize into a mesh; Factor XIIIa then cross-links the fibrin polymers to stabilize the clot.
AACC Hematology & Coagulation 2
Which coagulation factor is deficient in classic Hemophilia A?