What is antithrombin?
Antithrombin is a protein produced in the liver and is also called antithrombin III or antithrombin 3 (AT III for short). It plays an important role in hemostasis. While it has little effect on primary hemostasis, it can effectively inhibit secondary hemostasis (blood clotting):
Antithrombin ensures the degradation of thrombin (Factor IIa) – a clotting factor that leads to the cleavage of fibrin monomers and thus the formation of a stable clot for the purpose of hemostasis. In addition, the protein also inhibits other clotting factors and enzymes and ensures the formation of tissue-type plasminogen activator (t-PA) in the vessel walls. t-PA also inhibits blood clotting.
With the help of the drug heparin, the effect of antithrombin can be increased approximately 1000-fold. That is why heparin is used as an anticoagulant.
When is antithrombin determined?
Antithrombin deficiency leads to vascular blockage due to excessive clotting. Therefore, the amount and activity of antithrombin 3 are determined in cases of thrombosis of unknown cause. Antithrombin deficiency is congenital.
In addition, the measurement of antithrombin can be useful in so-called consumption coagulopathy. This is a severe clinical picture in which, usually due to shock or sepsis, the coagulation system is activated in an uncontrolled manner. Small clots (microthrombi) form in the vessels, while at the same time there is heavy bleeding because the clotting factors are depleted.
Antithrombin is also measured when heparin therapy is unsuccessful.
Antithrombin – normal values
If there is an antithrombin deficiency, this is referred to as type I AT deficiency. If, on the other hand, the activity of the protein is reduced, this is referred to as type II AT deficiency. The following normal values apply:
|
concentration |
18 – 34 mg/dl |
|
Activity |
70 – 120 % of the norm |
Values may differ with respect to sex and age. In newborns up to three months of age, antithrombin has no disease value.
When are antithrombin levels too low?
Congenital antithrombin deficiency is very rare. Much more common is high consumption of antithrombin due to consumption coagulopathy, thrombosis, bleeding, or surgery. Heparin treatment also decreases the measured value. In addition, a formation disorder, for example in the context of liver cirrhosis or other liver diseases, also leads to an antithrombin deficiency.
When are antithrombin levels too high?
What to do in case of altered antithrombin levels?
In the case of elevated measured values, the treatment of the underlying disease is paramount. Antithrombin deficiency should also always be clarified by a doctor and carefully treated. Those affected suffer thromboses much more frequently, which is why substitution with artificial antithrombin is usually unavoidable.
