[A new test for evaluating the von Willebrand factor: collagen-induced agglutination of fixed thrombocytes].

In primary hemostasis von Willebrand factor (vWf) promotes the adhesion of platelets to subendothelial structures of the damaged blood vessel. A new test is described which measures the collagen binding affinity of vWf. Activities of vWf in plasmas of 51 patients were measured with either collagen (ColCof) or ristocetin (RCof). Regression-analysis showed a good correlation of both activities (r = 0.924). In a second group of 21 patients with a variant of von Willebrand's disease, ColCof activity was generally higher than RCof activity.