Blood coagulation factor VIII (Factor VIII (FVIII))

Blood coagulation factor VIII is an essential glycoprotein involved in the intrinsic pathway of blood clotting. It circulates in plasma bound to von Willebrand factor in an inactive form. Upon vascular injury, it becomes activated and dissociates from von Willebrand factor. Activated FVIII serves as a critical cofactor for activated Factor IX (IXa), forming the intrinsic tenase complex on platelet surfaces that catalyzes the conversion of Factor X to its active form Xa—an essential step leading to fibrin clot formation. The protein is encoded by the F8 gene, primarily produced by liver sinusoidal cells and endothelial cells throughout the body. Deficiency or dysfunction due to mutations in F8 results in hemophilia A, characterized by impaired blood clotting and excessive bleeding. Therapeutic administration of recombinant or plasma-derived FVIII can restore hemostasis but may be complicated by immune responses generating neutralizing antibodies (“inhibitors”). Elevated endogenous levels are associated with increased thrombotic risk. Factor VIII does not possess enzymatic activity itself but functions as a non-catalytic cofactor within multi-protein complexes during hemostasis. Its structure includes multiple domains that interact with other proteins such as von Willebrand factor and are targets for pathogenic antibody inhibitors—a significant challenge during replacement therapy.

Other names

Antihemophilic factorAHFF8Coagulation factor VIII, procoagulant componentProcoagulant component

Replacement therapy supplies functional FVIII to restore clotting in hemophilia A patients; FVIII acts as a cofactor for activated Factor IX, enabling conversion of Factor X to Xa in the intrinsic pathway of blood coagulation