Antithrombin III
Last reviewed: 23.04.2024
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The reference values (norm) of the content of antithrombin III in blood plasma are 80-120%.
Antithrombin III is a glycoprotein, the most important natural inhibitor of blood coagulation; inhibits thrombin and a number of activated clotting factors (Xa, XIIa, IXa). Antithrombin III forms a high-speed complex - heparin-ATIII - with heparin. The main site for the synthesis of antithrombin III is the liver parenchyma cells.
Deficiency of antithrombin III can be primary (hereditary) and secondary, associated with a particular disease or condition. Acquired deficiency of antithrombin III may be due to reduced synthesis, increased consumption or loss of protein.
Reduction of antithrombin III concentration - a risk factor for thrombosis; can develop with the following conditions and diseases:
- atherosclerosis, in old age;
- in the middle of the menstrual cycle, in the last months of pregnancy;
- in the postoperative period;
- with liver diseases (chronic hepatitis, cirrhosis of the liver, the level of antithrombin III decreases in proportion to the severity of the disease);
- with acute DVS-syndrome (early and important laboratory test);
- with the introduction of heparin (since antithrombin III combines with heparin, with a low content of antithrombin III, heparin therapy is ineffective);
- when taking oral contraceptives and estrogens;
- shock conditions in which the production of antithrombin III falls sharply in the liver and its inhibitors are activated in the blood (the most common cause of the decrease in the concentration of antithrombin III).
An increase in the concentration of antithrombin III in the blood is regarded as a risk factor for bleeding and is noted in the following cases:
- with viral hepatitis, cholestasis, severe acute pancreatitis, pancreatic cancer;
- with a deficiency of vitamin K;
- when receiving anticoagulants of indirect action;
- during menstruation.
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