The functional activity of von Willebrand factor (VWF) is most frequently measured by using the ristocetin cofactor assay (VWF:RCo). However, the method's drawbacks include unsatisfactory precision, sensitivity and availability of automated system applications. We have developed an alternative assay (INNOVANCE VWF Ac*) that is based on the binding of VWF to recombinant glycoprotein Ib (GPIb). Two gain-of-function mutations were introduced into a GPIb fragment, allowing an assay format without ristocetin. Fully automated assay applications are available for the BCS/BCS XP systems and the Sysmex CS-2000i*, Sysmex CA-7000, Sysmex CA-1500 and Sysmex CA-560 systems.
The INNOVANCE VWF Ac* assay measuring range extends from 4 to 600% VWF for all systems except the Sysmex CA-560 system. Within-device precision values were found to be between 2 and 7%. The limit of detection was below 2.2% VWF. In a study on the BCS XP system, a total number of 580 sample results yielded a correlation to the VWF:RCo assay of r equal to 0.99 (slope = 0.96). Very similar results were observed when von Willebrand disease samples type 1, 2A, 2B, 2M, 2N and 3 were investigated with the new assay and the VWF:RCo assay. The excellent performance data and comparability to VWF:RCo, together with the ease of use, led us to the conclusion that the ristocetin cofactor assay can be replaced by the new GPIb-binding assay to reliably diagnosing patients with von Willebrand disease.
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