A Reliable von Willebrand Factor: Ristocetin Cofactor Enzyme-Linked Immunosorbent Assay to Differentiate between Type 1 and Type 2 von Willebrand Disease

von Willebrand disease (vWD) is the most common hereditary bleeding disorder due to either a qualitative or a quantitative defect in von Willebrand factor (vWF). vWF is a multimeric plasma protein that plays an important role in (1) primary hemostasis, by sustaining indirect platelet adhesion especially at high shear rates, and in (2) secondary hemostasis, by protecting factor VIIIc (FVIIIc) from degradation. A correct diagnosis of vWD is based on the accurate identification of one of the six different subtypes (type 1, 2A, 2B, 2M, 2N, 3). To do this, different laboratory tests are available. One aspect of the identification is the discrimination between type 1 and type 2 (2A, 2B, and 2M) vWD. In type 1 vWD, both vWF levels (vWF:Ag) and vWF activity (vWF:RCof) are decreased; in type 2, the vWF:Ag level is normal or decreased and vWF:RCof is decreased. Thus, ratios of vWF:Ag to vWF:RiCof above 1 allow identifation of type 2 vWD patients. The currently used vWF:RCof test is an agglutination test in which patients' plasma is added to washed fixed control platelets in the presence of ristocetin and the extent of agglutination is measured. This test suffers from high interlaboratory and intralaboratory variability. We have recently shown that the same vWF:RCof can also be measured in an enzyme-linked immunosorbent assay (ELISA) with a low interassay and intraassay variability and can be used to identify patients suffering from vWD. We here show that our test allows the discrimination between type 1 and type 2 vWD patients.