hematology and oncology
Antithrombin Deficiency
Diagnosis of Antithrombin Deficiency
Laboratory testing is done for patients with an unexplained blood clot and involves quantification of the capacity of patient plasma to inhibitthrombinin the presence ofheparin.Heparinnormally inhibits coagulation by accelerating inactivation ofthrombinby antithrombin. In patients with antithrombin deficiency, inactivation ofthrombinis reduced. The residualthrombinin the test mixture is inversely proportional to the functional antithrombin concentration in the patient's plasma. Antithrombin protein levels also can be measured with immunologic assays, but these tests only measure the amount of antithrombin protein in the sample and cannot assess the function of this protein. Since rare patients with antithrombin deficiency express dysfunctional antithrombin proteins, activity assays are favored over antigen assays for the diagnosis of antithrombin deficiency. 