Evaluation of metabolic acidosis in patients with a kidney graft: Comparison of the bicarbonate-based and strong ion-based methods

Background: According to the traditional bicarbonate-based approach, metabolic acidosis is highly prevalent in kidney transplant recipients. However, the bicarbonate-based approach has been questioned by intensivists using strong ion difference-based methods. Methods: We compared the results obtained by the strong ion-based with the traditional approach based on bicarbonate among a cohort of 83 kidney transplant recipients. Results: Fifty-five percent of the patients were acidotic based on venous bicarbonate (effective) (effective were linearly correlated (r = 0.94; P <.0001), with a slope close to 1. A greater percentage of patients presented with an increase in unexplained anions by the strong ion gap (SIG) than by the anion gap corrected (AG_corrected) method (42 vs 32%, respectively). AG_corrected and SIG were directly related (r = 0.919; P <.0001), but the best fit of the relationship was polynomial with a progressively greater effect on SIG with increased AG_corrected, suggesting that as anions progressively accumulate, their detection by SIG increases. By multiple regression analysis, plasma chloride, potassium, uric acid, and phosphate predicted blood bicarbonate. Analogously, chloride, potassium and uric acid predicted SID_effective. Age was a predictor of changes in AG_corrected, whereas age and plasma urea predicted SIG. Conclusions: The use of the SID yielded results that were similar to the traditional bicarbonate-based approach. Conversely, SIG appeared to be more sensitive than AG for detection of anion accumulation among patients with a kidney graft.