WHAT IS VON WILLEBRAND FACTOR ANTIGEN (VWF AG, FACTOR VIII R : AG, FACTOR VIII–RELATED ANTIGEN) TEST?
von Willebrand’s disease is an autosomal dominantly transmitted factor VIII defect. It is a coagulation disorder that results in varying degrees of bleeding abnormalities. Coagulation factor VIII has three properties, namely, procoagulant activity (circulating von Willebrand factor is newly recognized as initiating platelet adhesion), antigenic activity, and von Willebrand factor activity. In this test, factor VIII antigenic activity is determined by measurement of von Willebrand factor antigen (vWF Ag). In haemophilia A and in carriers of haemophilia A, vWF Ag activity is normal, but in von Willebrand’s disease, vWF Ag is characteristically low (that is, <40% of control sample activity).