What hematological change is typically seen with Hemophilia A (factor VIII deficiency)?

Hemophilia A is caused by a deficiency in von Willebrand factor and factor VIII, which plays a crucial role in the intrinsic pathway of the coagulation cascade. The intrinsic pathway influences the activated partial thromboplastin time (APTT or PTT), which measures the time it takes for blood to clot. Since factor VIII is specifically involved in this pathway, a deficiency leads to an elevation in PTT. This is a key diagnostic marker for Hemophilia A.

In contrast, prothrombin time (PT) assesses the extrinsic pathway and is usually normal in patients with Hemophilia A, as they do not have deficiencies in factors associated with that pathway. A decreased platelet count would typically be associated with thrombocytopenia rather than a primary defect in the coagulation cascade, and increased fibrinogen levels are often seen in conditions that promote clotting or inflammation, neither of which is directly relevant to a deficiency of factor VIII. Thus, elevated PTT is the most indicative change seen in Hemophilia A.