Evaluation of an heterogeneous group of patients with von Willebrand disease using an assay alternative to ristocetin induced platelet agglutination.

ABSTRACT

BACKGROUND: Diagnosis of von Willebrand disease (VWD) type 2 usually relies on the discrepancy between the von Willebrand factor (VWF) ristocetin cofactor activity (VWFRCo) and VWF antigen (VWFAg). Type 2B patients can be discriminated from other qualitative VWD variants by using ristocetin-induced platelet agglutination (RIPA) test. The major limitation of RIPA is the requirement of fresh blood sample. OBJECTIVES: In this study, we evaluated the VWF gain-of-function mutant GPIb binding (VWFGPIbM) and VWFRCo assays to investigate whether the VWFGPIbM/VWFRCo ratio was able to identify the type 2B variant among an heterogeneous VWD population, previously characterized following the ISTH-SSC guidelines. PATIENTS/METHODS: Seventy-six VWD patients and 31 healthy subjects were evaluated by using VWFAg, VWFRCo, and VWFGPIbM assays. RESULTS: The mean (minimum-maximum values) VWFGPIbM/VWFRCo ratio was higher in type 2B patients (2.53, 0.84-6.11) than in healthy controls (1.05, 0.87-1.34), type 1 (0.85, 0.51-1.15), 2A (1.20, 0.36-2.82), and 2M (1.07, 0.91-1.38) (P < 0.0001). Type 2B variants were divided into four groups (A, B, C, and D) according to their different multimeric patterns. The mean value of the VWFGPIbM/VWFRCo ratio in the four groups showed an increasing trend from group A (1.08) to D (3.69), proportional to the loss of high molecular weight multimers. Among 32 type 2B patients, previously diagnosed with RIPA, 8 (mainly with a type I New York/Malmö phenotype) were not confirmed using the VWFGPIbM/VWFRCo ratio. CONCLUSIONS: Whenever the RIPA test is not feasible, the VWFGPIbM/VWFRCo ratio might help to identify severe type 2B VWD patients.