von Willebrand factor is important for platelet-platelet & platelet-vessel hemostatic interactions. Decreased vWF antigen is seen in Congenital von Willebrand disease (vWD) and in acquired conditions associated with monocloncal gammopathies, lymphoproliferative disorders and autoimmune diseases. This assay is useful for the diagnosis of vWD and its subtyping. It also helps in differentiating vWD from Hemophilia A. The assay is also useful for monitoring therapeutic efficacy of treatment with vWF concentrates.