Calculation of plasma chloride levels using blood gas measurements

Chloride is the major plasma anion. There are several methods available for the determination of serum chloride levels. Unfortunately these methods are sometimes not available in the urgent setting where values are needed. Here we describe a formula for estimating plasma chloride levels.
Fifty-two consecutive patients were enrolled for which serum chloride levels were estimated using the formula CL- = (Na 10 –TBB), and also measured directly through the colorimetric method. Correlation between the two values was analyzed using Pearson correlation coefficient and agreement was shown in the Bland-Altman plot.
Comparing the values achieved through estimation and laboratory determination of plasma chloride revealed a significant correlation (r = 0.97). Consistent agreement was described within -4.8 and .6 on the Bland-Altman plot throughout the measurements.
The formula presented here may be a reliable alternative to direct measurement of serum chloride when direct results are not available.