Antithrombin (AT; Antithrombin III) deficiency is described as an AT activity level that is consistently less than 80% of normal (or the lower limit of the assay's reference range). It can be inherited or acquired. Some patients may experience a higher chance of thromboembolism due to AT deficiency. Replacement therapy is now feasible thanks to the availability of plasma-derived AT concentrates and recombinant AT, but their authorised use is only for people who have hereditary AT deficiency.
