Ristocetin induced platelet agglutination

The ristocetin induced platelet aggregation (RIPA) is an in vitro assay for von Willebrand factor activity used to diagnose von Willebrand disease. It has the benefit over the ristocetin cofactor activity in that it can diagnose type 2B vWD and Bernard-Soulier syndrome.

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In an unknown fashion, the antibiotic ristocetin causes von Willebrand factor to bind the platelet receptor glycoprotein Ib (GpIb), so when ristocetin is added to normal blood, it causes agglutination. In von Willebrand disease, where von Willebrand factor is absent or defective, abnormal agglutination occurs:

• In type 1 vWD: no agglutination occurs
• In type 2A vWD: no agglutination occurs
• In type 2B vWD: hyperactive agglutination occurs
• In type 2N vWD: normal agglutination occurs
• In type 3 vWD: no agglutination occurs