A patient with hemophilia requires pre-operative laboratory evaluation. Which test is most relevant?

Correct answer: B. Partial thromboplastin time (PTT)

• A. INCORRECT. PT (prothrombin time) evaluates the extrinsic coagulation pathway (factors VII, X, V, II, fibrinogen). It is most relevant for monitoring warfarin therapy. PT is not directly affected in classical hemophilia.
• B. CORRECT. PTT (partial thromboplastin time) evaluates the intrinsic coagulation pathway. Hemophilia A (factor VIII deficiency) and Hemophilia B (factor IX deficiency) both involve deficiencies in the intrinsic pathway, resulting in a prolonged PTT with a normal PT. PTT is the most relevant and diagnostic test for hemophilia.
• C. INCORRECT. INR is a standardized form of PT used to monitor warfarin anticoagulation. It evaluates the extrinsic pathway and is not the relevant test for hemophilia, which affects the intrinsic pathway.
• D. INCORRECT. Platelet count evaluates the quantitative aspect of primary hemostasis. Hemophilia is a coagulation factor deficiency that does NOT affect platelet number or primary hemostasis. Platelet count is normal in hemophilia.