antithrombin

Any substance that inhibits or prevents the effects of thrombin in such a manner that blood does not coagulate. A deficiency of a. results in impaired inhibition of coagulation factors IIa, IXa, and Xa in plasma, causing recurrent thrombosis.

- a. III a plasma α₂-globulin process that inhibits thrombin and has anticoagulant activities. Deficiency [MIM*107300] is commonly inherited as an autosomal dominant trait, caused by mutation in a. III gene (AT₃) or chromosome 1q; this is one of the few known mendelizing disorders from which thrombotic disease occurs.

- normal a. an a. naturally occurring in blood and certain tissues under normal conditions in contrast to abnormal states or a. from other sources.

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an·ti·throm·bin -'thräm-bən n any of a group of substances in blood that inhibit blood clotting by inactivating thrombin compare ANTIPROTHROMBIN, HEPARIN

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an·ti·throm·bin (an″te-thromґbin) [anti- + thrombin] any naturally occurring or therapeutically administered substance that neutralizes the action of thrombin and thus limits or restricts blood coagulation. Six naturally occurring antithrombins have been designated by Roman numerals I to VI; antithrombins I and III are the most common and significant ones. Heparin is also considered an antithrombin.