Abstract
［Aim］ We examined whether a multi‒item automatic biochemical analyzer (BAA) based on the ion‒selective electrode (ISE) dilution method is suitable for measuring dialysate electrolyte levels. ［Method］ The Na, K, and Cl concentrations (mEq/L) of a dialysate containing 140 mEq/L Na, 2.0 mEq/L K, 112.25 mEq/L Cl, and 27.5 mEq/L HCO3 were measured 10 times using the serum (s) and urine (u) modes of the BAA. The concentrations of a control substance for ensuring accurate dialysate measurements (JCTCM330), which contained 140 mEq/L Na, 1.96 mEq/L K, 109.8 mEq/L Cl, and 28.5 mEq/L HCO3, and physiological saline were measured in triplicate in the same way. ［Results］ The following Na, K, and Cl concentration measurements were obtained for the dialysate, JCTCM330, and physiological saline using s‒mode and u‒mode, respectively (mEq/L)： dialysate： Na： 139.2 and 138.7 (p＜0.05), K： 2.02 and 2.10 (p＜0.0005), Cl： 110.1 and 112.7 (p＜0.0001)； JCTCM330： Na： 139.1 and 138.4, K： 1.96 and 2.00, Cl： 106 and 108.7； saline： Na： 152.3 and 151.8, K： 0.37 and 0.20, Cl： 150.8 and 152.4. In both modes, the Na, K, and Cl measurements were close to the expected values. S‒mode, which was calibrated with standard serum, produced higher Na values and lower Cl values than u‒mode. ［Discussion］ ISE measure ion activity. The ion concentration is obtained by dividing the ion activity by the relevant ionic activity coefficient. We assume that the measured values were close to the expected values because diluting the sample brought the activity coefficient close to 1 and the proportion of solid components in serum close to 0. Higher Na and lower Cl levels were seen in s‒mode because s‒mode is calibrated with standard serum. ［Conclusion］ The BAA at our hospital is suitable for obtaining dialysate electrolyte measurements, but u‒mode produces lower Na levels, and s‒mode produces lower Cl levels.
