Antithrombin III test

Antithrombin (a naturally occurring mild blood thinner) is a protein produced by the liver that plays an important role in regulating blood clots.

The antithrombin III test measures the activity (function) and amount of antithrombin in the blood. The aim of the test is to find out the cause of recurrent thrombosis (blood clots).

During the blood clotting process, blood clotting enzymes are activated, causing a so-called protein fibre to form a network, which stops the bleeding. Coagulation occurs only at the site of injury, as anti-coagulation mechanisms also play a role in the process, preventing the blood from coagulating throughout the body. In severe cases, blood clotting can occur without injury. In this case, a blood clot forms inside the blood vessel, blocking the blood flow.

A few months after the development of the blood clot or if the patient does not respond as expected to heparin anticoagulation therapy.

Heparin is an anticoagulant polysaccharide (the most negatively charged molecule in the human body). Anticoagulation covers oral medication or, in the case of heparin, intravenous administration.

A blood sample taken from a vein is needed for the test.

Decreased activity or amount may indicate type 1 antithrombin deficiency. In this case, the reason for the decrease in activity is that less antithrombin is available to control blood clotting.

Decreased activity and normal antithrombin antigen levels may indicate type 2 antithrombin deficiency. In this case, the amount of antithrombin protein is sufficient but does not work properly. The patient’s predisposition to clotting is increased in both cases.

If antithrombin activity is adequate, an antithrombin antigen test is usually not performed. In this case, there may be another disease in the background.

The test alone does not constitute a diagnosis. In all cases, please consult the specialist or internist who ordered the test with the result.