Why this test?
To determine whether the amount of functional antithrombin III in the blood is normal (before the antigen test).
For examination of patients whose body does not react normally to heparin.
Antithrombin III is synthesized mainly in vascular endothelium and liver. Blood is thin due to anticoagulants, one of which is antithrombin III, which blocks clotting factors. Usually, when a vessel is damaged, the body activates a series of coagulation factors (coagulation cascade) in order to form a blood clot and prevent further blood loss.
Antithrombin III helps regulate this process by slowing the action of several coagulation factors, including thrombin, as well as factors Xa, IXa, and Xia, which are designed to prevent extra clots from forming. Patients with antithrombin III deficiency are at risk for thrombosis. Inherited deficiency is rare (1 case in 5000 patients). If the patient has a genetic predisposition, thrombotic episodes usually make themselves felt already in 20-30 years.
There are two types of antithrombin III deficiency. With the first, normal antithrombin III is produced, but in insufficient quantities. With the second type, it is produced in sufficient quantities, but at the same time it is dysfunctional.
A decrease in the level of antithrombin III can be caused by the following reasons:
-congenital deficiency of antithrombin III,
-liver disease with impaired liver function (cirrhosis, cancer),
-nephrotic syndrome (diseases with a significant loss of protein in the urine),
-massive thrombosis (for example, pulmonary embolism),
-major surgical interventions,
-use of large doses of oral contraceptives,
-long-term administration of heparin,
-CVD syndrome (a sharp violation of all blood coagulation processes, which can occur in many critical conditions: shocks, severe injuries, burns, massive thrombosis, etc.),
-an oncological disease.
Regardless of the reasons for insufficient content of antithrombin III, its main manifestation is recurrent arterial and venous thrombosis. Hereditary deficiency of antithrombin III is especially characteristic of frequent myocardial infarctions and strokes at a young age.