Coagulation Factor VIII, also known as FVIII and F8, is a member of the multicopper oxidase family. Coagulation Factor VIII is a cofactor for factor IXa which, in the presence of Ca+2 and phospholipids, converts factor X to the activated form Xa. It contains 3 F5/8 type A domains, 2 F5/8 type C domains and 6 plastocyanin-like domains. FVIII is synthesized in the liver, and perhaps in other tissues. It is a coagulation cofactor which circulates bound to von Willebrand factor and is part of the intrinsic coagulation pathway. It is a macromolecular complex composed of two separate entities, one of which, when deficient, results in hemophilia A, and the other, when deficient, results in von Willebrand"s disease. Hemophilia A is a disorder of blood coagulation characterized by a permanent tendency to hemorrhage. About 5% of patients have severe hemophilia resulting in frequent spontaneous bleeding into joints, muscles and internal organs. Less severe forms are characterized by bleeding after trauma or surgery.

coagulation factor VIII, procoagulant component