American Board of Internal Medicine (ABIM) Certification Practice Exam

Hemophilia A and B typically produce a prolonged what?

1. Prothrombin time

2. Activated partial thromboplastin time

3. D-dimer test

4. International normalized ratio

The correct answer is: Activated partial thromboplastin time

Hemophilia A and B are both bleeding disorders that result from deficiencies in clotting factors. Hemophilia A is due to a deficiency of factor VIII, while Hemophilia B is due to a deficiency of factor IX. Both of these factors are part of the intrinsic pathway of the coagulation cascade. The activated partial thromboplastin time (aPTT) test evaluates the functionality of the intrinsic and common clotting pathways. In cases of hemophilia, where there is a deficiency of factor VIII or factor IX, the aPTT becomes prolonged because the necessary factors for efficient clot formation are lacking, leading to a delay in the formation of a fibrin clot. In contrast, the prothrombin time (PT) assesses the extrinsic pathway and common pathway, and is primarily affected by factors that do not include factor VIII or IX. Therefore, the PT is usually normal in hemophilia. The D-dimer test is used primarily to evaluate for thrombotic disorders and is not directly relevant to hemophilia. The International Normalized Ratio (INR) also derives from the prothrombin time and would not typically be prolonged in hemophilia. Overall, the prolongation of activated partial thromboplastin time