WHAT IS VON WILLEBRAND FACTOR ACTIVITY (RISTOCETIN COFACTOR) TEST?
Von Willebrand’s disease is an autosomal dominantly transmitted factor VIII defect. It is a coagulation disorder that results in varying degrees of bleeding abnormalities. Coagulation factor VIII has three properties, namely, procoagulant activity (low or absent in haemophilia A), antigenic activity, and von Willebrand factor activity. The von Willebrand factor activity of factor VIII enhances the formation of platelet plugs. In this test, the von Willebrand factor activity of factor VIII is measured by use of a modified platelet aggregation test. In normal clients or those with haemophilia A, the antibiotic ristocetin induces platelet aggregation on a test sample. In clients with von Willebrand’s disease, however, the addition of ristocetin to the client’s serum does not result in platelet aggregation. The lower the percentage of platelet aggregation, the lower the amount of von Willebrand factor.