Antithrombin III

Reference values (norm) for antithrombin III content in blood plasma are 80-120%.

Antithrombin III is a glycoprotein, the most important natural inhibitor of blood coagulation; it inhibits thrombin and a number of activated coagulation factors (Xa, XIIa, IXa). Antithrombin III forms a fast-acting complex with heparin - heparin-ATIII. The main site of synthesis of antithrombin III is the cells of the liver parenchyma.

Deficiency of antithrombin III may be primary (hereditary) or secondary, associated with a specific disease or condition. Acquired deficiency of antithrombin III may be due to decreased synthesis, increased consumption, or loss of the protein.

A decrease in the concentration of antithrombin III is a risk factor for thrombosis; it can develop in the following conditions and diseases:

• with atherosclerosis, in old age;
• in the middle of the menstrual cycle, in the last months of pregnancy;
• in the postoperative period;
• in liver diseases (chronic hepatitis, liver cirrhosis; the level of antithrombin III decreases in proportion to the severity of the disease);
• in acute DIC syndrome (early and important laboratory sign);
• when heparin is administered (since antithrombin III binds to heparin; with low antithrombin III levels, heparin therapy is ineffective);
• when taking oral contraceptives and estrogens;
• shock conditions in which the production of antithrombin III by the liver drops sharply and its inhibitors are activated in the blood (the most common reason for a decrease in the concentration of antithrombin III).

An increase in the concentration of antithrombin III in the blood is considered a risk factor for bleeding and is noted in the following cases:

• for viral hepatitis, cholestasis, severe acute pancreatitis, pancreatic cancer;
• in case of vitamin K deficiency;
• when taking indirect anticoagulants;
• during menstruation.

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