Use Factor VIII (FVIII) is an essential blood Clotting protein also known as anti-hemophilic factor (AHF). In humans, factor VIII is encoded by the F8 gene Defects in this gene results in hemophilia, a Recessive X-linked coagulation disorder. Factor VIII is produced in liver sinusoidal cells and endothelial cells outside of the liver throughout the body. This protein circulates in the bloodstream in an inactive form, bound to another molecule called Von Willebrand Factor, until an injury that damages blood vessels occurs. In response to injury, coagulation factor VIII is activated and separates from von Willebrand factor.