A 25-year-old man has a lifelong history of mucosal bleeding, prolonged bleeding time, normal platelet count, and normal PT/aPTT. Platelet aggregation is absent with ADP, collagen, and epinephrine but normal with ristocetin. Which platelet surface protein is deficient?

• A Glycoprotein Ib/IX/V complex
• B Von Willebrand factor
• C Glycoprotein IIb/IIIa (integrin αIIbβ3) ✓
• D Glycoprotein Ia/IIa

Explanation

Absent aggregation with all agonists except ristocetin is diagnostic of Glanzmann thrombasthenia, caused by deficiency or dysfunction of GPIIb/IIIa. GPIIb/IIIa is the fibrinogen receptor required for platelet aggregation. Ristocetin-induced agglutination is mediated by VWF binding to GPIb/IX/V, which remains intact in Glanzmann. Bernard-Soulier shows the opposite pattern: absent ristocetin response with giant platelets.

Reference: Hoffbrand's Postgraduate Haematology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.