Factor VIII (aka Factor VIII, FVIII) is an essential clotting factor. The lack of normal FVIII causes Hemophilia A, an inherited bleeding disorder.
The gene for Factor VIII is located on the X chromosome (Xq28).
Factor VIII is a glycoprotein procofactor synthesized and released into the bloodstream by the liver. In the circulating blood, it is mainly bound to von Willebrand factor (vWF, also known as Factor VIII-related antigen) to form a stable complex. Upon activation by thrombin or factor Xa, it dissociates from the complex to interact with Factor IXa the coagulation cascade. It is a cofactor to Factor IXa in the activation of Factor X, which in turn, with its cofactor Factor Va, activates more thrombin. Thrombin cleaves fibrinogen into fibrin which polymerizes and crosslinks (using Factor XIII) into a blood clot.
No longer protected by vWF, activated Factor VIII is proteolytically inactivated in the process (most prominently by activated Protein C and Factor IXa) and quickly cleared from the blood stream.
Factor VIII harvested from donated blood (or more likely, purchased blood plasma) or Recombinant Factor VIII can be given to hemophiliacs to restore hemostasis. Thus, Factor VIII is also known as Anti-Hemophilic Factor.
DiaPharma sells Chromogenix Coamatic Factor VIII, Chromogenix Coatest SP Factor VIII (formerly Coatest FVIII), Chromogenix Coatest SP4 Factor VIII (formerly Coatest Factor VIII:C/4)
Sources: DiaPharma, Wikipedia, PubMed