Laboratory diagnosis and monitoring of desmopressin treatment of von Willebrand's disease by flow cytometry

BACKGROUND AND OBJECTIVES: von Willebrand's disease (VWD) is a heterogeneous bleeding disorder caused by quantitative or qualitative defects in von Willebrand factor (VWF). The diagnosis of VWD requires several laboratory tests. The aim of our study was to validate a flow cytometric test for the diagnosis of VWD and for monitoring the effects of desmopressin therapy. DESIGN AND METHODS: Flow cytometric analysis of ristocetin-induced VWF binding to platelets was performed in platelet-rich plasma (PRP) samples from patients with VWD and from control subjects and in samples of formalin-fixed platelets in the presence of plasma from patients or controls. In 12 VWD patients the test was conducted before and 1 hour after desmopressin infusion. Results were compared with VWF:Ag, VWF:RCo, VWF:CB, RIPA, PFA-100 and the skin bleeding time. RESULTS: Ristocetin-induced VWF binding to platelets, evaluated by both flow cytometry-based assays, was significantly reduced in patients with type1, 2A and 2M VWD as compared with that in healthy subjects. Patients with type 2B VWD showed reduced binding of VWF to formalin-fixed platelets, but increased binding to autologous platelets in PRP, similar to RIPA. VWF binding to platelets assessed by both flow cytometric assays correlated significantly with VWF:Ag, VWF:RCo, VWF:CB, RIPA, PFA100 and bleeding time. VWF binding to platelets increased after desmopressin infusion. INTERPRETATION AND CONCLUSIONS: The measurement of ristocetin-induced binding of VWF to platelets by flow cytometry is a sensitive, simple and rapid test for the diagnosis of VWD and for the monitoring of the effects of desmopressin therapy. The flow cytometric assay performed with autologous platelets is useful in the identification of type 2B VWD patients.