Coagulation factors

Coagulation factors are a group of proteins involved in the blood clotting process. They are traditionally numbered using Roman numerals (I through XIII, with no Factor VI) and many also have common names. These factors can be classified into three main groups: the fibrinogen group (including Factors I, V, VIII, and XIII), the prothrombin group (including Factors II, VII, IX, and X), and the contact group. Most coagulation factors are serine proteases that circulate as inactive zymogens until activated during the coagulation cascade. Exceptions include tissue factor, Factor V, Factor VIII, and Factor XIII, which are not serine proteases. Many factors (II, VII, IX, and X) are vitamin K-dependent, requiring vitamin K for post-translational modification that converts specific glutamate residues to gamma-carboxyglutamate residues, making them functionally active. The coagulation cascade is traditionally divided into intrinsic (contact activation) and extrinsic (tissue factor) pathways, both converging on a common pathway. The intrinsic pathway includes Factors XII, XI, IX, and VIII, while the extrinsic pathway involves Factor VII and tissue factor. The common pathway includes Factors X, V, II (prothrombin), and I (fibrinogen). When vascular injury occurs, subendothelial collagen and von Willebrand factor are exposed, initiating platelet adhesion and activation. This is followed by the activation of coagulation factors in a cascade-like manner, ultimately resulting in the conversion of fibrinogen to fibrin and the formation of a stable clot. Deficiencies or dysfunctions of coagulation factors can lead to bleeding disorders, such as hemophilia A (Factor VIII deficiency) and hemophilia B (Factor IX deficiency), while certain mutations like Factor V Leiden can predispose individuals to thrombosis.

Other names

Clotting factorsBlood coagulation factorsHemostatic factors

Proteolytic activation of downstream factors, cofactor activity in enzymatic complexes, conversion of fibrinogen to fibrin, cross-linking of fibrin polymers.