Diagnosis or Exclusion of von Willebrand Disease Using Laboratory Testing.

von Willebrand disease (VWD) is a common bleeding disorder diagnosed based on clinical features and following laboratory testing. VWD is due to deficiencies or defects in the plasma protein von Willebrand factor (VWF), a large adhesive protein with multiple activities. Laboratory testing therefore centers on assessment of VWF protein level using VWF antigen (VWF:Ag), as well as assays that measure VWF activity, most notably platelet glycoprotein (GP) Ib and collagen binding (VWF:CB) activities. Decreases in VWF:Ag and VWF activities, as well as the pattern of such changes, help define VWD and its type. Classically, the most often used assay for measuring GPIb binding activity was the ristocetin cofactor assay (VWF:RCo), which historically measured agglutination of fixed human platelets by VWF in the presence of ristocetin. This assay is now often replaced or supplemented with other assays based on binding of VWF to recombinant GPIb, generally without the use of platelets, and with or without ristocetin. This chapter briefly reviews laboratory tests for VWD, as well as recommended approaches to use of such assays to help diagnose or exclude VWD in patients showing clinical features.