Ristocetin-induced aggregation of gel filtered platelets a study of von Willebrand's disease and the effect of aspirin

Automated assays for von Willebrand factor activity

von Willebrand factor (VWF) ristocetin cofactor activity (VWF:RCo) by platelet aggregometry has been considered the gold standard for evaluating the ability of VWF to bind platelets for over 40 years. Many automated systems no longer require platelets and rather rely on agglutination of latex particles. Automated methods of measuring VWF activity have improved performance characteristics and are performed on the same coagulation instruments used for routine testing via immunoturbidimetric methodology. Alternatively, a newer chemiluminescence assay system for measuring VWF activity demonstrates excellent performance characteristics. As these methods are becoming widely used, it is important to assess their performance in diagnosing and monitoring different types of von Willebrand disease. We review the automated methodologies and the published performance of these VWF assays. Advantages and limitations of these automated methods are discussed.

Von Willebrand's disease: combined qualitative and quantitative abnormalities

Studies of von Willebrand's disease typically show either a quantitative or a qualitative abnormality of the factor VIII/von Willebrand factor protein. In studies of five patients we found a combination of quantitative and qualitative defects. Quantitative abnormalities included decreased levels of procoagulant, antigen and von Willebrand factor activities in the plasma and in the column fractions of cryopercipitate from gel chromatography. Qualitative abnormalities included annormal migration or shape of the crossed antigen-antibody arcs, disproportionate reduction of von Willebrand factor in relation to antigen, altered gel elution patterns of procoagulant, and von Willebrand factor activities the negative carbohydrate stain of the VIII protein on polyacryl-amide-gel electrophoresis and, in two patients, a decreased sialic acid content of factor VIII protein. Our studies indicate that von Willebrand's disease comprises both quantitative and qualitative defects.