Sulfatide-Binding Assay for von Willebrand Factor: Detection of von Willebrand's Disease without Discrimination of vWD Subtypes

Abstract

The appropriate diagnosis of von Willebrand's disease requires a panel of laboratory assays. Subclassification of a patient's von Willebrand's disease is also important as it will influence management. The minimal test panel should comprise an assay for factor VIII coagulant, assessment of von Willebrand factor antigen and at least one functional von Willebrand factor assay (collagen-binding assay and/or Ristocetin cofactor assay). This panel will provisionally determine whether von Willebrand's disease is present and whether the von Willebrand's disease provisionally detected is a qualitative (Type 2) or quantitative (Types 1 or 3) defect, and results will help guide further investigation and the need for further testing. In view of reports indicating that sulfatides bind to von Willebrand factor by a specific high-affinity mechanism distinct from collagen, and with affinity reportedly dependent on von Willebrand factor size, the author has devised and tested a novel enzyme linked immunosorbant assay (ELISA)-based von Willebrand factor sulfatide-binding assay for its potential use in von Willebrand's disease diagnosis and von Willebrand's disease subtype discrimination. Results obtained using this assay were compared with those using a standard von Willebrand factor antigen assay (by ELISA), a Ristocetin cofactor assay for von Willebrand factor (by platelet agglutination procedure), and a collagen-binding assay for von Willebrand factor (by ELISA). All four von Willebrand factor assays were capable of detecting von Willebrand factor in a dose-dependent manner (i.e., were von Willebrand factor quantitative), and all were capable of detecting deficiencies in von Willebrand factor associated with von Willebrand's disease (i.e., all could detect the presence of von Willebrand's disease; Type 1 and Type 2 von Willebrand's disease). Linear regression analysis showed good correlation of results of sulfatide-binding assay for von Willebrand factor with results of the von Willebrand factor antigen R=0.939, p<0.0001 , Ristocetin cofactor assay for von Willebrand factor R=0.819, p<0.0001 , and collagen-binding assay for von Willebrand factor R=0.802, p<0.0001 . However, only the collagen-binding assay for von Willebrand factor and Ristocetin cofactor assay for von Willebrand factor could detect the presence of von Willebrand factor functional discordance associated with Type 2 von Willebrand's disease. That is, in the current study, the sulfatide-binding assay for von Willebrand factor yielded laboratory data for von Willebrand's disease patients that was essentially similar to that obtained using the von Willebrand factor antigen assay, and which therefore could not be used to discriminate between von Willebrand's disease subtypes.