Medical Emergencies · single question
Which laboratory test should be performed to assess clotting function in a hemophiliac patient?
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Correct answer: A. Partial Thromboplastin Time (PTT/aPTT)
Partial Thromboplastin Time — aPTT (A) is the primary test for hemophilia. Hemophilia A (Factor VIII) and B (Factor IX) are deficiencies in the intrinsic pathway of coagulation. The aPTT specifically measures the intrinsic pathway. In hemophilia, aPTT is PROLONGED while PT/INR is normal.
• INR / PT (B, C): measure the extrinsic pathway (Factor VII, X, V, II, fibrinogen) — affected by warfarin, liver disease. Normal in hemophilia.
• CBC (D): counts blood cells including platelets — useful for thrombocytopenia but does NOT measure clotting factor function.
• Clinical pearl: Normal PT + elevated aPTT = intrinsic pathway defect = think hemophilia A or B, or heparin therapy.
• INR / PT (B, C): measure the extrinsic pathway (Factor VII, X, V, II, fibrinogen) — affected by warfarin, liver disease. Normal in hemophilia.
• CBC (D): counts blood cells including platelets — useful for thrombocytopenia but does NOT measure clotting factor function.
• Clinical pearl: Normal PT + elevated aPTT = intrinsic pathway defect = think hemophilia A or B, or heparin therapy.
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