WHO/BS/2018.2337 Proposal for standardization of methods for von Willebrand factor binding to recombinant Glycoprotein Ib - an International Reference Reagent for VWF:GPIbM and VWF:GPIbR methods

Overview

Diagnosis of the bleeding disorder, von Willebrand disease (VWD), includes measurement of von Willebrand factor (VWF) binding to the glycoprotein Ib (GPIb) receptor on the platelet surface. The original method used to measure this activity, the ristocetin cofactor method (VWF:RCo), is associated with large variability and poor sensitivity. In recent years alternative methods have been developed based on the binding of VWF to recombinant GPIb. These methods either rely on the presence of ristocetin for VWF binding (VWF:GPIbR) or employ a "gain-of-function" mutant of GPIb which does not require ristocetin for VWF binding (VWF:GPIbM). Increasing use of these new methods has raised an urgent need for their standardization at the international level in order to support the harmonization of test results and prevent divergence between laboratories which could arise if locally derived units were used. As a result of discussions within the VWF sub-committee of the International Society on Thrombosis and Haemostasis (ISTH) it was agreed to propose assigned values to the WHO 6th IS Factor VIII / von Willebrand factor, plasma (07/316) as described below. This proposal was formally endorsed by the Scientific and Standardization Committee (SSC) of ISTH at the Board meeting held in Dublin, Ireland on 19 July 2018.