A 1-year-old boy with knee swelling after a couple of days that is warm to touch and painful; mother reports easy bruising. Which laboratory finding would you expect?

A 1-year-old boy with knee swelling after a couple of days that is warm to touch and painful; mother reports easy bruising. Which laboratory finding would you expect?

• A. Prolonged aPTT
• B. Prolonged bleeding time
• C. Prolonged PT
• D. Prolonged thrombin time

Answer: (A)

The scenario points to bleeding into a joint (hemarthrosis) in a young boy, which is classic for a deficiency in the intrinsic coagulation pathway, most often Hemophilia A or B. The test that specifically reflects the intrinsic pathway is the activated partial thromboplastin time; in these conditions the aPTT is prolonged because factors VIII or IX are deficient, slowing down the intrinsic pathway. The extrinsic pathway, measured by PT, remains normal because factor VII and the extrinsic pathway are unaffected. Bleeding time tends to be normal in hemophilia since platelet function and primary hemostasis are intact, and thrombin time is typically normal unless there’s another fibrinogen-related issue or heparin effect. So a prolonged aPTT best fits this presentation as the expected lab finding.

The scenario points to bleeding into a joint (hemarthrosis) in a young boy, which is classic for a deficiency in the intrinsic coagulation pathway, most often Hemophilia A or B. The test that specifically reflects the intrinsic pathway is the activated partial thromboplastin time; in these conditions the aPTT is prolonged because factors VIII or IX are deficient, slowing down the intrinsic pathway. The extrinsic pathway, measured by PT, remains normal because factor VII and the extrinsic pathway are unaffected. Bleeding time tends to be normal in hemophilia since platelet function and primary hemostasis are intact, and thrombin time is typically normal unless there’s another fibrinogen-related issue or heparin effect. So a prolonged aPTT best fits this presentation as the expected lab finding.