What is the typical lab finding in mild hemophilia A?

• A. Prolonged aPTT with normal PT; reduced factor VIII activity
• B. Normal aPTT and normal factor VIII
• C. Elevated fibrinogen
• D. Prolonged PT with normal aPTT

Answer: (A)

Hemophilia A involves a deficiency of factor VIII, a crucial cofactor in the intrinsic coagulation pathway. Factor VIII partners with IXa to activate X; when it’s reduced, the intrinsic cascade is slowed, lengthening clot formation time measured by the activated partial thromboplastin time (aPTT). In mild cases, factor VIII activity is decreased but not absent, typically in the 5–40% range, so the aPTT is prolonged. The prothrombin time (PT) assesses the extrinsic pathway and the common pathway, which remain normal because factor VII and the extrinsic pathway aren’t affected by factor VIII deficiency. Therefore, the classic lab picture is a prolonged aPTT with a normal PT, and a reduced factor VIII activity on specific assays. Elevated fibrinogen isn’t characteristic of mild hemophilia A.