In hemophilia, which laboratory finding is typically prolonged?

In hemophilia, which laboratory finding is typically prolonged?

• A. aPTT
• B. PT
• C. Platelet count
• D. INR

Answer: (A)

Hemophilia affects factors in the intrinsic coagulation pathway, so the intrinsic cascade is defective and the time to form a fibrin clot lengthens. The aPTT specifically evaluates the intrinsic pathway (factors XII, XI, IX, and VIII) and the common pathway, so a deficiency here prolongs the aPTT. In contrast, the extrinsic pathway is assessed by the PT (and INR), and those values remain normal because factor VII is not impaired in classic hemophilia. Platelet count reflects platelets, not coagulation factor activity, so it is typically normal in isolated hemophilia. Thus, the lab finding that is typically prolonged is the aPTT.

Hemophilia affects factors in the intrinsic coagulation pathway, so the intrinsic cascade is defective and the time to form a fibrin clot lengthens. The aPTT specifically evaluates the intrinsic pathway (factors XII, XI, IX, and VIII) and the common pathway, so a deficiency here prolongs the aPTT. In contrast, the extrinsic pathway is assessed by the PT (and INR), and those values remain normal because factor VII is not impaired in classic hemophilia. Platelet count reflects platelets, not coagulation factor activity, so it is typically normal in isolated hemophilia. Thus, the lab finding that is typically prolonged is the aPTT.