[Von Willebrand factor and Von Willebrand disease]

Von Willebrand factor (VWF) is a multimeric adhesive protein that binds platelets to exposed subendothelium and carries factor VIII in the circulation. VWD is classified into three major subtypes, distinguished by a quantitative deficiency of VWF (type 1: partial deficiency; type 3: complete deficiency) or qualitative defects of VWF (type 2A, 2B, 2M and 2N). Its diagnosis is based on both clinical and laboratory criteria. The severity of bleeding varies considerably depending on the level of VWF and the FVIII reduction. Diagnosis is especially difficult in patients with a mild or dubious phenotype (type 1 and 2 VWD). Laboratory strategy includes screening tests: complete blood count, platelet morphology, prothrombin time (PT), activated partial thromboplastin time (aPTT) and platelet function analysis. The next step is measurement of VWF antigen, VWF activity and FVIII activity, and calculating ratios between antigen and activity. Finally, multimers, the affinity of VWF for platelets or FVIII can be analysed.