Which finding would support a diagnosis of hemophilia A?

The correct answer is supported by the understanding of hemophilia A, which is a genetic disorder that affects blood coagulation. Specifically, hemophilia A results from a deficiency in factor VIII, a crucial clotting protein that plays a vital role in the coagulation cascade.

A prolonged activated partial thromboplastin time (aPTT) specifically indicates a difficulty in the intrinsic pathway of coagulation, which primarily involves factors like factor VIII. In patients with hemophilia A, the absence or insufficiency of factor VIII leads to a longer aPTT, as the blood takes longer to clot due to the impaired function of this specific coagulation factor. This finding is a hallmark of hemophilia A and is critical for confirming the diagnosis.

In contrast, thrombocytopenia, which refers to a low platelet count, can lead to bleeding but is not specific to hemophilia A. Hematuria, or the presence of blood in urine, can be a consequence of bleeding disorders but does not definitively indicate hemophilia A by itself. Neither of these findings directly correlate with the underlying pathology of hemophilia A as clearly as a prolonged aPTT does. Therefore, the presence of a prolonged aPTT is a clear and