Pathology · single question
In a patient with hemophilia, which laboratory test is MOST appropriate for diagnosis and monitoring?
Show answer and explanation
Correct answer: B. Partial Thromboplastin Time (PTT/aPTT)
- A. INR (based on PT) measures the EXTRINSIC coagulation pathway (Factors VII, X, V, II, I) — used to monitor warfarin therapy. Normal in hemophilia A and B.
- B. Partial Thromboplastin Time (aPTT) measures the INTRINSIC coagulation pathway (Factors VIII, IX, XI, XII). Hemophilia A (Factor VIII deficiency) and Hemophilia B (Factor IX deficiency) both prolong the aPTT while PT/INR remains normal. aPTT is the correct diagnostic and monitoring test.
- C. Prothrombin Time (PT) measures the extrinsic pathway — normal in hemophilia.
- D. Platelet count measures the number of platelets — normal in hemophilia (which is a clotting factor deficiency, not a platelet problem).