A 5-year-old girl with recurrent epistaxis and easy bruising has prolonged bleeding time, normal platelet count, and normal PT. aPTT is mildly prolonged. Which additional finding best supports a diagnosis of von Willebrand disease?

• A Reduced platelet aggregation with ADP
• B Absent factor IX activity
• C Positive lupus anticoagulant
• D Reduced ristocetin cofactor activity ✓

Explanation

Von Willebrand disease causes defective platelet adhesion through failure of vWF to bind subendothelium and platelet GPIb, demonstrated functionally by reduced ristocetin cofactor activity or impaired agglutination with ristocetin. The prolonged bleeding time with normal platelet count reflects this adhesion defect, and mild aPTT prolongation comes from low factor VIII carried by vWF. ADP induced aggregation is abnormal in platelet secretion disorders such as storage pool disease, not in vWF deficiency.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.