factor VII

Factor VII is synthesized in the liver and requires vitamin K-dependent gamma-carboxylation (along with factors II, IX, X, and proteins C and S) for activity. Upon vascular injury, tissue factor (thromboplastin) exposed on subendothelial cells binds circulating factor VII, forming the TF-VIIa complex, which activates factor X (and IX) to initiate the coagulation cascade (extrinsic pathway). This TF-VIIa-Xa complex rapidly generates a small burst of thrombin, which amplifies the cascade via activation of factors V, VIII, and XI (intrinsic pathway), leading to the large thrombin burst needed for stable clot formation. Because factor VII has the shortest half-life (~4-6 hours) among the coagulation factors, it is the first to decrease with vitamin K antagonist therapy (warfarin) or in vitamin K deficiency/liver disease, causing an early rise in PT/INR before other factors are affected. Clinical correlations: Congenital factor VII deficiency is a rare autosomal recessive bleeding disorder presenting with variable bleeding tendency (from mucocutaneous bleeding to severe hemorrhage) and isolated prolonged PT with normal PTT. Recombinant activated factor VII (rFVIIa, NovoSeven) is used clinically to treat bleeding in hemophilia patients with inhibitors and in factor VII deficiency. PT (prothrombin time) is the lab test that specifically assesses the extrinsic pathway (factor VII) and common pathway (factors X, V, II, fibrinogen); it is used to monitor warfarin therapy. Factor VII deficiency or dysfunction leads to prolonged PT with normal PTT, while PTT remains normal because the intrinsic pathway (XII, XI, IX, VIII) is unaffected.