Understanding Hemophilia A: A Diagnostic Perspective

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

• A. Prolonged partial thromboplastin time
• B. Prolonged prothrombin time
• C. Reduction in factor IX activity
• D. Reduction in von Willebrand factor

Answer: (A)

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

When it comes to pediatric health, especially in the realm of genetic disorders, clarity is key. If you’re studying for the Rosh Pediatrics Exam, understanding the nuances of hemophilia A is essential—both for your exam and for any future patient interactions. So, let’s break down a common scenario you might encounter: a male infant with a subgaleal hematoma, born to a mother who’s a carrier of hemophilia A. What does this mean, and what should you look for?

You might be wondering, “What diagnostic findings should I pay attention to in this case?” That’s a great question! The critical answer here revolves around the prolonged partial thromboplastin time (PTT). This finding is like a flashing neon sign, signaling the potential presence of hemophilia A. Now, why is this finding so specific and significant?

Hemophilia A is essentially a genetic hiccup. It results from a deficiency in factor VIII, a protein that's crucial for blood coagulation. Think of factor VIII as a key player in a sports team—without it, the rest of the team (the coagulation cascade) just can’t function correctly. When factor VIII is in short supply, as in hemophilia A, it causes delays in the blood clotting process, leading to that troublesome prolonged PTT you’ll want to look out for.

Now, let’s discuss what happens when you see a prolonged PTT. It typically means that the intrinsic pathway of the clotting process is not working properly. Since this infant's mother carries the gene for hemophilia A, this prolonged PTT is a strong indicator that the infant may have inherited this condition. It serves as a simplistic yet effective diagnostic marker.

But what about the other options? You might see prolonged prothrombin time (PT) on the list, but don’t be fooled! This is associated with problems in the extrinsic pathway, often involving factor VII, which has nothing to do with hemophilia A. If you were to see a reduction in factor IX activity, that’d point you straight to hemophilia B, a different ballgame altogether. And let’s not forget about von Willebrand factor; a reduction there indicates von Willebrand disease—you guessed it, not hemophilia A.

In summary, when you think about hemophilia A, keep that prolonged PTT in your toolkit. It’s not just a lab result; it’s a powerful piece of the diagnostic puzzle. It’s vital knowledge as you prepare for the exam, and even more so as you step into the real world of pediatric care.

Now that we’ve unraveled this topic a bit, you may wonder about the broader implications. Understanding the coagulation cascade and its disorders can help shape your approach to various pediatric conditions. It’s about building a comprehensive view of how genetics, maternal health, and laboratory findings intertwine in the journey of diagnosing and treating young patients.