Which lab findings are characteristic of Hemophilia A?

Which lab findings are characteristic of Hemophilia A?

• A. Low Factor VIII with prolonged PTT; mixing study with normal plasma will correct
• B. Decreased Factor IX with prolonged PTT
• C. Low Factor VIII with normal PTT
• D. Low Factor VIII with prolonged PT

Answer: (A)

Hemophilia A is a deficiency of factor VIII in the intrinsic coagulation pathway, so the activated partial thromboplastin time (aPTT) is prolonged while the prothrombin time (PT) is usually normal. A mixing study—mixing patient plasma with normal plasma—helps distinguish true factor deficiency from an inhibitor. In factor VIII deficiency, the aPTT tends to correct toward normal after mixing because the normal plasma supplies the missing factor VIII. So the characteristic lab pattern is low factor VIII with prolonged aPTT, and correction on mixing with normal plasma, with a normal PT. Decreased factor IX would point to Hemophilia B, not A; a low VIII with a normal PTT doesn’t fit because VIII deficiency prolongs the aPTT; and a low VIII with a prolonged PT would imply involvement of the extrinsic pathway, which is not typical for Hemophilia A.

Hemophilia A is a deficiency of factor VIII in the intrinsic coagulation pathway, so the activated partial thromboplastin time (aPTT) is prolonged while the prothrombin time (PT) is usually normal. A mixing study—mixing patient plasma with normal plasma—helps distinguish true factor deficiency from an inhibitor. In factor VIII deficiency, the aPTT tends to correct toward normal after mixing because the normal plasma supplies the missing factor VIII. So the characteristic lab pattern is low factor VIII with prolonged aPTT, and correction on mixing with normal plasma, with a normal PT. Decreased factor IX would point to Hemophilia B, not A; a low VIII with a normal PTT doesn’t fit because VIII deficiency prolongs the aPTT; and a low VIII with a prolonged PT would imply involvement of the extrinsic pathway, which is not typical for Hemophilia A.