Comparison of Hypertonic and Isotonic Reference Electrode Junctionsfor Measuring Ionized Calcium in Whole Blood: A Clinical Study

We measured ionized calcium concentrations in whole blood from 91 patients who had no clinical or biochemical evidence of disturbed calcium homeostasis and who had a wide range of serum albumin concentrations. We used both a standard Ciba-Corning 634 analyzer, which has a membrane-restricted saturated KCI reference electrode bridge, and a modified instrument with a 150 mmol/L NaCI bridge. After adjusting the externally standardized values from each instrument for their least-squares regressions on pH, there was a significant correlation between ionized calcium and albumin only with the standard analyzer. In contrast, only values from the modified instrument corre-lated with serum chloride; this was not explained by ionic strength or organic anion interferences. We conclude that there is unlikely to be any major advantage in using