From the Research
Antithrombin activity levels below 87% suggest increased clotting risk in patients with antithrombin deficiency, with risk becoming particularly significant at levels below 70%. Patients with levels between 70-87% may require prophylactic anticoagulation during high-risk situations such as surgery, pregnancy, or prolonged immobility, while those with levels below 70% often warrant consideration of long-term anticoagulation therapy. The severity of thrombotic risk increases as antithrombin levels decrease, with those below 30% facing substantially higher risk. Antithrombin functions as a natural anticoagulant by inhibiting thrombin and other clotting factors, particularly factor Xa. When deficient, this regulatory mechanism is compromised, creating a prothrombotic state. Clinical decision-making should incorporate not only the antithrombin level but also the patient's personal and family history of thrombosis, presence of additional thrombotic risk factors, and the type of antithrombin deficiency (type I quantitative or type II qualitative) 1.
Some key points to consider when evaluating antithrombin activity levels include:
- The use of direct oral anticoagulants (DOACs) may cause false negative results of antithrombin deficiency screening, but the application of DOAC-Stop enables reliable evaluation of AT deficiency screening in patients taking rivaroxaban or apixaban and tested using the FXa-based method 2.
- Warfarin use does not increase the level of antithrombin in patients receiving the drug 3.
- Hereditary antithrombin deficiency is a rare, underrecognized medical condition that is associated with inadequate endogenous anticoagulation thought to result from impaired inhibition of serine protease coagulation factors, and maintaining adequate levels of AT during high-risk periods is an important treatment goal 4.
- Direct thrombin inhibitors, such as argatroban, seem to be suitable alternatives for acute anticoagulation in patients with antithrombin deficiency 5.
Regular monitoring of antithrombin levels is important for patients with known deficiency, especially when making decisions about anticoagulation management. The goal of treatment for patients with hereditary AT deficiency is an initial increase in AT activity to > or = 120% of normal levels followed by maintenance of AT activity at > or = 80% of normal levels 4.