Platelet-dependent von Willebrand factor activity : nomenclature and methodology : communication from the SSC of the ISTH

von Willebrand disease (VWD) is the most common bleeding disorder in man [1]. Measuring VWF functional activity is critical for making the correct diagnosis and classification. Traditionally considered the ‘gold standard’ for evaluating platelet-dependent VWF function, the ristocetin cofactor activity (VWF:RCo) assay was developed after the discovery of platelet aggregation by ristocetin. Imprecision and insensitivity of the VWF:RCo assay led to the development of new assays. Some of the issues related to VWF activity testing have recently been reviewed [7–11]. Because it is critical that users of these various assays recognize differences between details of functions being measured, a new nomenclature was developed by the VWF Subcommittee of the Standardization and Scientific Committee (SSC) of the International Society for Thrombosis and Haemostasis (ISTH). The guiding principles in developing a practical and accurate nomenclature included simplicity, consistency and accuracy. The result of this effort reached consensus and was formally approved by the VWF Subcommittee at the Milwaukee SSC Meeting on 23 June 2014