antithrombin

antithrombin I fibrin, referring to the capacity of fibrin to adsorb thrombin and thus neutralize it.

antithrombin III a naturally occurring inhibitor of blood coagulation; it is an α₂-globulin member of the serpin group, synthesized in the liver and found in the plasma and various extravascular sites. It inactivates thrombin as well as certain coagulation factors and kallikrein. Inherited deficiency of the protein, an autosomal dominant disorder, is associated with recurrent deep vein thrombosis and pulmonary emboli. Complications from the disorder are prevented and, in conjunction with heparin, treated with a preparation of antithrombin III from pooled human plasma, administered intravenously.

Any substance that counters the effect of thrombin, an enzyme that converts fibrinogen into fibrin, leading to blood coagulation.