Which lab result is expected for Hemophilia A when performing a mixing study?

Which lab result is expected for Hemophilia A when performing a mixing study?

• A. Prolonged PTT that corrects with mixing study
• B. Prolonged PT unaffected by mixing
• C. Thrombocytopenia
• D. Normal PTT

Answer: (A)

Mixing studies distinguish a true factor deficiency from an antibody inhibitor. In Hemophilia A, the intrinsic pathway is missing factor VIII, so the PTT is prolonged. When patient plasma is mixed with normal plasma, the donated factor VIII from the normal plasma corrects the deficiency, and the PTT returns toward normal. Therefore the expected result is a prolonged PTT that corrects with mixing. If an inhibitor were present, the PTT would not correct (or would show only partial correction after incubation).

Mixing studies distinguish a true factor deficiency from an antibody inhibitor. In Hemophilia A, the intrinsic pathway is missing factor VIII, so the PTT is prolonged. When patient plasma is mixed with normal plasma, the donated factor VIII from the normal plasma corrects the deficiency, and the PTT returns toward normal. Therefore the expected result is a prolonged PTT that corrects with mixing. If an inhibitor were present, the PTT would not correct (or would show only partial correction after incubation).