A 2-year-old boy presents with recurrent swelling of the left knee and right elbow without trauma. There is no family history of bleeding, but his maternal uncle reportedly died young of uncontrolled bleeding. PT is normal, PTT is prolonged and corrects fully on mixing studies. Which investigation will best establish the diagnosis?

• A Bleeding time
• B von Willebrand factor antigen and ristocetin cofactor activity
• C Factor XIII assay
• D Factor VIII assay ✓

Explanation

Recurrent hemarthroses with an X-linked pedigree, normal PT, and prolonged PTT corrected by mixing point to a single-factor deficiency, classically hemophilia D. The definitive test is a specific factor VIII assay, which also grades severity: less than 1% is severe, 1 to 5% moderate, above 5% mild. Ristocetin studies diagnose von Willebrand disease, which typically gives mucosal rather than joint bleeding. Bleeding time is normal in hemophilia and adds nothing diagnostically.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.