Rosh Pediatrics Practice Exam

A male infant born to a mother who is a carrier of hemophilia A has a subgaleal hematoma. Which diagnostic finding supports hemophilia A?

1. Prolonged partial thromboplastin time

2. Prolonged prothrombin time

3. Reduction in factor IX activity

4. Reduction in von Willebrand factor

The correct answer is: Prolonged partial thromboplastin time

Hemophilia A is a genetic disorder caused by a deficiency in factor VIII, which is a crucial component of the blood coagulation cascade. One of the key laboratory findings in individuals with hemophilia A is an abnormality in the partial thromboplastin time (PTT), specifically a prolonged PTT. This occurs because factor VIII plays an important role in the intrinsic pathway of the coagulation process, and its deficiency leads to difficulties in the formation of blood clots. In this scenario, the infant's prolonged partial thromboplastin time would indicate that the intrinsic pathway is affected, aligning with the diagnosis of hemophilia A, especially given the mother's carrier status. The other options indicate issues that are not specific to hemophilia A. Prolonged prothrombin time (PT) is associated with deficiencies in the extrinsic pathway factors or factors that affect the common pathway, such as factor VII, which are not related to hemophilia A. A reduction in factor IX activity would point towards hemophilia B, which is a separate condition. Finally, a reduction in von Willebrand factor is indicative of von Willebrand disease rather than hemophilia A. Therefore, the finding of a prolonged partial thromboplastin time is