<prompt> 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?abnormal factor VIII functiondecreased levels of functional factor VIIIdecreased factor IX leveldecreased von Willebrand factor  <response>: 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. 