Which laboratory finding will be abnormal in a child with hemophilia?

• A. The platelet count
• B. The hemoglobin level
• C. The white blood cell count
• D. The partial thromboplastin time (PTT)

Answer: (D)

Hemophilia is a deficiency of intrinsic pathway coagulation factors (such as factor VIII or IX). The test that reflects this pathway is the partial thromboplastin time (PTT), so when intrinsic factors are lacking, the PTT is prolonged. Platelet count remains normal because platelets and primary hemostasis are not the primary problem in hemophilia, and white blood cell count is not affected by this bleeding disorder. Hemoglobin might decrease with ongoing bleeding, but that is a secondary effect rather than a diagnostic feature. Therefore, the abnormal lab finding you’d expect is an increased PTT.