ABSTRACT

Various prothrombotic (e.g. von Willebrand factor, platelet activating factor) and antithrombotic (e.g. nitric oxide, tissue plasminogen activator) factors are involved in the above response.

The clotting cascade involves a variety of coagulation factors and two distinct pathways (extrinsic and intrinsic) that come together as the final common pathway and result in the formation of cross-linked fibrin that stabilizes the platelet plug to form a clot. Heparin exerts its antithrombotic effect by inhibiting the intrinsic pathway, and warfarin works by inhibiting the extrinsic pathway. The activated partial thromboplastin time (APTT) is a measure of intrinsic function and is therefore increased by heparin therapy. The prothrombin time (PT) and the international normalized ratio (INR) are measures of extrinsic function and are increased by warfarin.