Abstract
Endotoxin (ET) levels in the dialysate must be determined by an accurate and precise assay. For validation, three commercial kits, Endospecy (Seikagaku, Tokyo), ET single test-ES (Wako, Osaka) and Kinetic QCL (BioWhittacker, Maryland) were tested for interference. The dilution series of the dialysate, bicarbonate and acid concentrate were made between 1- and 80-fold, which were spiked with U.S. Pharmacopoeia reference standard ET (USP RSE). The recovered activity for ET in each series was evaluated versus the theoretical value of 50EU/L. The dilutions which overcame interference with Endospecy were 1, 40 and 20 in the dialysate, acid concentrate and bicarbonate, respectively. Likewise, 1:4, 1:40 and 1:40 dilutions were necessary to overcome inhibition with ET single test-ES. With Kinetic QCL, there was no interference in the undiluted dialysate; however, enhancement was observed between 2- and 16-fold dilution. The dilution which overcame interference in the bicarbonate was 40-fold with Kinetic QCL. Even the 80-fold dilution of the acid concentrate failed to overcome inhibition with Kinetic QCL. Clinical dialysate samples were also measured for ET activity by Endospecy and ET single test-ES kit in parallel. The ET single test-ES kit gave significantly lower values (44%) than the Endospecy kit (p<0.05). In addition, the stabilizing agent for preventing ET in the dialysate from loss of activity through inactivation and adsorption was shown to be effective, as the recovered ET activity in the dialysate was kept within the range of 100±25% of the initial value as long as 7 days.
