From the Research
High antithrombin (AT) activity indicates an increased level of this natural anticoagulant protein in the blood, which means the body has enhanced ability to prevent inappropriate blood clotting. This finding is relatively uncommon and generally not concerning. High AT activity may occur naturally in some individuals or can be caused by medications like estrogen-containing contraceptives. It might also be seen during pregnancy or in response to inflammation. Unlike low AT activity (which increases clotting risk), elevated AT activity rarely requires treatment unless it's causing bleeding problems. If bleeding occurs, treatment would focus on addressing the underlying cause rather than directly targeting the high AT levels. The clinical significance of high AT activity is limited because our bodies have multiple mechanisms to maintain proper clotting balance, and isolated elevation of this protein typically doesn't disrupt this balance enough to cause problems. Regular monitoring may be recommended if the elevation is substantial or if there are other risk factors for bleeding disorders, as noted in studies on antithrombotic therapy 1. It's also important to consider the effects of direct oral anticoagulants (DOACs) on antithrombin activity testing, as they may cause false negative results of antithrombin deficiency screening 2. However, the use of DOAC-Stop, an agent reversing in vitro effects of DOACs, can enable reliable evaluation of AT deficiency screening in patients taking rivaroxaban or apixaban and tested using the FXa-based method 2. Overall, high AT activity is not typically a cause for concern, and treatment should focus on addressing any underlying causes of bleeding problems rather than directly targeting the high AT levels.