IN-VITRO CHARACTERIZATION OF ANTITHROMBIN III CONCENTRATES - A SINGLE-BLIND STUDY

Twenty-three lots of five antithrombin III (AT III) concentrates from four manufacturers were analyzed in a single-blind study. Al the prepa rations had been virus-inactivated by pasteurization, and one concentr ate had also been treated with solvent/detergent (S/D). AT III activit ies were determined using two thrombin-based and one factor Xa-based c hromogenic substrate assays. AT III antigen was measured by kinetic ne phelometry. All AT III assays were tested against the first internatio nal reference preparation coded 72/1. In addition, AT III was characte rized by crossed immunoelectrophoresis in the presence of heparin and by gel filtration. The following were quantified: heparin cofactor II activity and antigen content, heparin activity, thrombin-AT III comple xes, AT III-protease complexes, total protein, albumin, immunoglobulin s, glucose and pH. The AT III concentrates differed markedly in terms of their purity and potency. The specific activities of AT III and the ratios of AT III activity to antigen content ranged from 3.4 to 6.9 a nd from 0.63 to 0.84, respectively. The highest values were found in f ive lots of the concentrate that had been treated by both pasteurizati on and S/D. This preparation was the only one that was virtually free of denaturated AT III, as judged by crossed immunoelectrophoresis. Mar ked batch-to-batch variation in AT III potencies was found in two out of the five preparations analyzed. In two out of five lots from one ma nufacturer, the measured potencies were more than 10% lower than the d eclared potencies. None of the analyzed preparations contained heparin cofactor II, and heparin activities were very low in all lots.