Laboratory and clinical evaluation of an assay of thrombin-antithrombin III complexes in plasma.

We evaluated a recently developed commercial assay for quantifying thrombin-antithrombin III (TAT) complexes in human plasma. The assay is precise (within-assay CV less than 10%, between-assay CV less than 13%), and sensitive (detection limit 0.7 micrograms of TAT per liter of plasma). Measurements for healthy volunteers yielded a normal reference (95 percentile) interval of 0.8 to 5.0 micrograms/L (n = 50, mean 2.1 micrograms/L, range 1.1 to 7.5 micrograms/L). TAT concentrations were increased in 25 of the 41 patients who fulfilled the clinical criteria of disseminated intravascular coagulation (DIC, overall mean 15.8 micrograms/L) and in 30 of the 35 patients with deep-vein thrombosis of the leg (overall mean 9.4 micrograms/L). We assessed the accuracy of the TAT assay by comparison with established criteria for the laboratory diagnosis of DIC involving various cutoff values for antithrombin III, factor V, fibrinogen, platelet count, fibrin/fibrinogen degradation products, and activated partial thromboplastin time. The low specificity of the TAT assay with regard to some of these criteria indicates that the latter are probably insensitive.