Kidney Res Clin Pract.  2020 Dec;39(4):441-450. 10.23876/j.krcp.19.126.

Relationship between serum total carbon dioxide concentration and bicarbonate concentration in patients undergoing hemodialysis

• Hirai K
• Ookawara S
• Morino J
• Minato S
• Kaneko S
• Yanai K
• Ishii H
• Matsuyama M
• Kitano T
• Shindo M
• Miyazawa H
• Ito K
• Ueda Y
• Watano T
• Fujino S
• Omoto K
• Morishita Y

• KMID: 2509805
• DOI: http://doi.org/10.23876/j.krcp.19.126

Abstract

Background
Few studies have investigated the relationship between serum total carbon dioxide (CO₂) concentration and bicarbonate ion (HCO₃^-) concentration in patients undergoing hemodialysis. We determined the agreement and discrepancy between serum total CO₂and HCO₃^- concentrations 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 hemodialysis patients.
Methods
One hundred forty-nine arteriovenous blood samples from 84 hemodialysis patients were studied. Multiple linear regression analysis was used to determine factors correlated with HCO₃^- concentration. Diagnostic accuracy of serum total CO₂ was evaluated using receiver operating characteristic curve analysis and a 2 × 2 table. Agreement between serum total CO₂ and HCO₃^- concentrations was assessed using Bland-Altman analysis.
Results
Serum total CO₂ concentration was closely correlated with HCO₃^- concentration (β = 0.858, P < 0.001). Area under the curve of serum total CO₂ for the identification of low and high bicarbonate concentrations was 0.989. Use of serum total CO₂ to predict low and high bicarbonate concentrations had a sensitivity of 100%, specificity of 50.0%, positive predictive value of 96.5%, negative predictive value of 100%, and accuracy of 96.6%. Bland-Altman analysis showed moderate agreement between serum total CO₂ and HCO₃^- concentrations. Discrepancies between HCO₃^- and serum total CO₂ concentrations (serum total CO₂ - HCO₃^- ≤ -1) were observed in 89 samples.
Conclusion
Serum total CO₂ concentration is closely correlated with HCO₃^- concentration in hemodialysis patients. However, there is a non-negligible discrepancy between serum total CO₂ and HCO₃^- concentrations.

Keyword

Acid base balance; Bicarbonate; Hemodialysis; Serum total carbon dioxide