Evaluation of an automated von Willebrand factor activity assay in von Willebrand disease.

ABSTRACT

We evaluated the use of the turbidimetric HemosIL von Willebrand Factor (VWF) Activity assay (VWFAct) on the STA-R automated coagulometer (Stago, Asnières, France) for the diagnosis of von Willebrand disease (VWD). For this, we prospectively screened 268 patients. As a second part, we retrospectively assayed 111 patients with well-defined VWD subtype. In the first prospective study, we demonstrate that in most cases of VWD, VWF ristocetin cofactor activity (VWFRCo) and VWFAct are highly correlated but that they both cannot be considered a good screening assay when used alone, since they could miss about 25% of VWF abnormalities. However, the association of VWFAct analysis and the Platelet Function Analyzer-100 (PFA-100) test constitutes an excellent screening strategy. In our second retrospective study concerning VWD subtypes, VWFRCo and VWFAct were well correlated but could be very discrepant, especially for some cases of type 2M VWD. We consider that VWFRCo remains the "reference assay" for VWD subtype classification.