A 4-year-old girl has recurrent epistaxis and easy bruising since early childhood. Her mother has a lifelong history of menorrhagia. Investigations show a normal platelet count, mildly prolonged aPTT that corrects on mixing, normal PT, and prolonged skin bleeding time. Factor VIII activity is reduced to 35 percent. Which additional test will confirm the diagnosis?

• A Ristocetin-induced platelet aggregation
• B von Willebrand factor antigen assay ✓
• C Bone marrow aspiration
• D Factor IX activity assay

Explanation

The autosomal dominant family history, mucosal bleeding pattern, low-normal platelet count, prolonged bleeding time, low factor VIII, and mildly prolonged aPTT point to von Willebrand disease. B reduced von Willebrand factor antigen confirms it. Ristocetin-induced aggregation tests platelet-type function and is abnormal in type 3 and some type 2 variants, but it is not the primary confirmatory assay. In hemophilia B the bleeding time is characteristically normal, which excludes that distractor here.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.