A 19-year-old man has had recurrent bleeding occur in his knee when playing contact sports. He has no history of spontaneous bleeding, but his brother had similar problems. Consultation with a specialist reveals that he has "mild" hemophilia A. Which of the following factor abnormalities is consistent with this diagnosis?: (A) abnormal factor VIII function, (B) decreased levels of functional factor VIII, (C) decreased factor IX level, (D) decreased von Willebrand factor
Answer is B. In hemophilia A, there are decreased levels of functioning factor VIII. This can be due to reduced amounts of normal VIII, the presence of a functionally abnormal protein, or a combination of both. The activated partial thromboplastin time (APTT) is prolonged, and the prothrombin consumption test is abnormal. The prothrombin time, thrombin clotting time, and bleeding time are usually normal.