PB0815 - Evaluation of the diagnostic accuracy of VWF:Ac and VWF Ristocetin Cofactor Activity in the diagnosis of von Willebrand disease

Background: VWF antigen (VWF:Ag) and Ristocetin Cofactor activity(VWF:RCo) are initial laboratory tests used in the diagnosis of von Willebrand disease(VWD). Due to the low reproducibility and sensitivity of the VWF:RCo test, the VWF:Ac test has emerged as an alternative diagnostic method, reflecting the binding of plateletGPIb receptors to VWF in the absence of ristocetin.

Aims: The aim of the study was to evaluate the performance of VWF:Ac Innovance (VWF:Ac) and VWF:RCo tests in measuring VWF activity, and to investigate the accuracy and the sensitivity in the diagnosis of VWD.

Methods: The study consisted 40 patients who have been diagnosed VWD previously and 20 healthy subjects. Plasma VWF:Ag, VWF:RCo, VWF:Ac, FVIII activity, platelet aggregation with 0.6mL/1,2mL ristosetin were measured using SysmexXN 6000 coagulation analyzer, and platelet count was measured by Beckman CoulterLH780 hematology analyzer.

Results: The comparison of VWF:RCo with VWF:Ac assay showed good agreement(y=5.4544 + 0.996x,mean bias:0.6). VWFAg levels of type1, type2 and 3 patients were lower than those of control group( p=0.000) being the lowest in type3 patients. VWF:RCo and VWF:Ac were also lower in all types of VWD compared with controls(p=0.011 for type1 and p=0.000 for type2 and 3),VWF:Ac and VWF:RCo in type3 patients were also different than type1(p=0.016, p0.034). FVIII levels were also significantly different than those of control, also,decreased FVIII was obtained in type3 VWD, compared to type1 and 2(p=0.046,p=0.006). Diagnostic value was evaluated by ROC curves; AUC was 0.662 for VWF:RCo/Ag and 0.548 for VWF:Ac/VWFAg for all group.

Conclusion(s): Our results indicate VWF:AC test showed good concordance and aggrement with VWF:RCo. However, we assumed that the VWF activity to antigen ratio had better diagnostic value for the classification of VWF deficiency.