Relationship Between Serum Total Carbon Dioxide Concentration and Bicarbonate Concentration in Patients Undergoing...

Background Few studies have assessed the relationship between serum total carbon dioxide (CO₂) and bicarbonate ion (HCO₃ ^-) concentration in patients undergoing peritoneal dialysis. We determined the agreement between serum total CO₂ and HCO₃ ^- concentration and the diagnostic accuracy of serum total CO₂ for the prediction of low (HCO₃ ^- <24 mEq/L) and high (HCO₃ ^- ≥24 mEq/L) bicarbonate concentrations in patients on peritoneal dialysis. Methods We collected 245 samples of venous blood from 51 patients on peritoneal dialysis. Independent factors that correlated with the HCO₃ ^- concentration were analyzed using multiple linear regression analysis. The diagnostic accuracy of serum total CO₂ was evaluated by receiver operating characteristic (ROC) curve analysis and a 2×2 table. Agreement between serum total CO₂ and HCO₃ ^- concentration was assessed by Bland-Altman analysis. Results Serum total CO₂ was independently correlated with HCO₃ ^- concentration (β = 0.354, p < 0.001). The area under the curve of serum total CO₂ for the identification of low and high bicarbonate concentrations was 0.909. The diagnostic accuracy of serum total CO₂ for the prediction of low and high bicarbonate concentrations was: sensitivity, 91.5%; specificity, 74.7%; positive predictive value, 53.5%; negative predictive value, 96.5%; and accuracy, 78.8%. Bland-Altman analysis showed a moderate agreement between serum total CO₂ and HCO₃ ^- concentration. Conclusion Serum total CO₂ correlated closely with the HCO₃ ^- concentration in patients undergoing peritoneal dialysis. Serum total CO₂ might be useful for predicting low and high bicarbonate in peritoneal dialysis patients.