The ratio of chloride to bicarbonate is a predictor of advanced metabolic acidosis in CKD stages G4 and G5

Metabolic acidosis is a common disorder in patients with chronic kidney disease (CKD). As eGFR decreases, a reciprocal decrease in bicarbonate (HCO₃^-) and an increase in chloride (Cl^-) concentration is observed. The aim of this study is to determine whether the Cl^-/HCO₃^- ratio can be used to predict metabolic acidosis with pH decline. A total of 115 patients (age 63 ± 17 years), with CKD stage G4 or G5 were enrolled in this cross-sectional study. The arterial (A) and venous (V) blood samples were taken during AV fistula creation and evaluated in a point of care testing analyzer. The ratio of arterial Cl^- and HCO₃^- concentration were calculated. According to mean arterial pH (pH-A) the group was divided into group with pH-A ≤ 7.33 and with pH-A > 7.33. The group with pH-A ≤ 7.33 showed significantly lower HCO₃^-, and higher Cl^-, Cl^-/HCO₃^--ratio than group with pH-A > 7.33. Cl^-/HCO₃^--A ratio negatively correlated with pH (r=-0.77,p < 0.01). The discriminative power of Cl^-/HCO₃^--A ratio for predicting pH-A ≤ 7.33 was 0.917 ([CI] = 0.87-0.97,p < 0.01) which provided 87% sensitivity and 84% specificity. The best cut-off was 6.22(mmol/l)/(mmol/l). In conclusion, a Cl^-/HCO₃^- ratio higher than 6.22(mmol/l)/(mmol/l) may be used as predictor of advanced metabolic acidosis in CKD stages G4 and G5.