An evaluation of antithrombin III laboratory tests.
Three laboratory tests for the measurement of antithrombin III (AT III) were evaluated. The tests measured functional AT III in serum and plasma, and the third measured AT III antigen in plasma. Normal values for each method were obtained by testing samples from 20 normal subjects. Each test was then performed on specimens from 15 patients clinically suspected of having hypercoagulable states. Each determination was run in duplicate. The hypercoagulable states included disseminated intravascular coagulation, pulmonary embolism, and pregnancy. Two-thirds of these patients were found to have antithrombin III levels below the normal range by all three of the methods studied. Patients who had decreased AT III activity in the functional assays also had decreased AT III antigen.