Abstract
Nguyen et al. concluded that the results of the Stewart-Fencl approach to the interpretation of acid-base status vary according to the analyzer used. This approach requires a number of analytical methods and can cumulate measurement errors.
It is uncertain whether this challenging approach offers more information than the traditional one introduced by Henderson-Hasselbalch combined with anion gap corrected for serum albumin concentration (AGcorr). We would like to draw attention to the importance of [Na+-Cl-] difference compared with [Na+] and [Cl-] evaluated separately.
The authors emphasized that [Na+] and [Cl-] are the most important variables in the calculation of the apparent strong anion difference (SIDapp), but they did not evaluate [Na+-Cl-] difference as a separate variable. Findings by Story et al. and our group indicate that this difference (lower limit 33 mmol/L in our laboratory) may decrease even if [Na+] and [Cl-] are within the normal range, because serum concentrations of these ions oscillate within a wide range of 10 mmol/L each.
Therefore, we propose that the variables of the traditional approach should be replaced by [Na+-Cl-] difference to detect the disturbance of acid-base status not caused by the retention of undetermined anions.