Clotting factors heparin affecting

Heparin inhibits reactions that lead to clotting, but does not significantly alter the concentration of the normal clotting factors of blood. Although clotting time is prolonged by full therapeutic doses, in most cases it is not measurably affected by low doses of heparin. Bleeding time is usually unaffected. 

The clotting cascade. Circles denote vitamin K dependent clotting factors, ovals are clotting factors affected by endothelial cell factors (e.g., thrombomodulin). Starred factors are inhibited by the actions of heparin and antithrombin III. 

Both drugs have an indirect action on the clotting cascade—heparin must form a complex with antithrombin III in order to produce an effect, and warfarin acts through depletion of vitamin K, which affects specific clotting factors. 

The conformational change in antithrombin III induced by heparin allows the molecule to bind to, and inactivate, factors involved in the clotting cascade. Primary factors affected are the activated forms of factor IX ( Christmas factor, or plasma thromboplastin component) and X ( Stuart-Prower factor ). 

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