Parallel determination of von Willebrand factor--Ristocetin and Botrocetin cofactors.

The quantitative determinations of von Willebrand Factor (vWF)-Ristocetin cofactor (vWF:RCof) and the Botrocetin cofactor (vWF:BCof) are important parameters for the diagnosis of von Willebrand's disease. These cofactors are usually determined in a platelet aggregometer using separate platelet reagents and assay protocols. We describe a method for the preparation of platelets made from outdated platelet concentrates and fixed with paraformaldehyde which agglutinate to ristocetin and to botrocetin. The platelet agglutination assay protocol has been simplified such that the same aggregometer instrument, platelet reagent, buffers and the reaction volumes can be used for parallel determination of vWF:RCof and vWF:BCof.