Clinical laboratory determination of antithrombin III. A new semi-automated method

A new, semi-automated method for determination of antithrombin III activity in the clinical laboratory is presented. The assay is performed utilizing the chromogenic substrate S-2238 and the ABA-100. Results are expressed in arbitrary units of activity; thus, construction of standard curves with interpolation of values is not necessary. The assay has a low day-to-day coefficient of variation (6%), is insensitive to heparin, and gives reliable results in a variety of clinical situations known to affect antithrombin III activity.