FaktorV

FaktorV, also known as Factor V, is a vitamin K–dependent coagulation factor produced by the liver. It circulates in the blood as an inactive procofactor and plays a central role in the coagulation cascade.

When activated by thrombin, Factor V is converted into Factor Va, a cofactor that, together with Factor Xa, forms the prothrombinase complex on phospholipid surfaces in the presence of calcium ions. This complex accelerates the conversion of prothrombin to thrombin, a key step in the formation of a fibrin clot.

Factor Va activity is regulated by the protein C pathway. Activated protein C, with its cofactor protein S, proteolytically inactivates Factor Va, reducing thrombin production. A common inherited variant, Factor V Leiden (Arg506Gln), makes Factor Va resistant to inactivation by activated protein C, thereby increasing the risk of venous thrombosis.

The F5 gene on chromosome 1 encodes Factor V. The protein is synthesized as a single polypeptide and, upon activation, is cleaved into heavy and light chains that compose its functional structure. Factor V deficiency is rare and can cause bleeding disorders, while acquired reductions may occur in liver disease or disseminated intravascular coagulation.

Clinically, Factor V Leiden is the most common hereditary thrombophilia in many populations and is assessed in evaluations of unexplained or recurrent venous thromboembolism. Management depends on individual risk and may involve anticoagulation during high-risk situations; Factor V status alone does not determine universal treatment.