Kidney Res Clin Pract.  2019 Sep;38(3):326-335. 10.23876/j.krcp.19.027.

Approximation of bicarbonate concentration using serum total carbon dioxide concentration in patients with non-dialysis chronic kidney disease

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

• KMID: 2457724
• DOI: http://doi.org/10.23876/j.krcp.19.027

Abstract

BACKGROUND
We investigated the relationship between serum total carbon dioxide (CO₂) and bicarbonate ion (HCO₃⁻) concentrations in pre-dialysis chronic kidney disease (CKD) patients and devised a formula for predicting low bicarbonate (HCO₃⁻< 24 mmol/L) and high bicarbonate (HCO₃⁻≥ 24 mmol/L) using clinical parameters.
METHODS
In total, 305 samples of venous blood collected from 207 pre-dialysis patients assessed by CKD stage (G1 + G2, 46; G3, 50; G4, 51; G5, 60) were investigated. The relationship between serum total CO₂ and HCO₃⁻ concentrations was analyzed using Pearson's correlation coefficient. An approximation formula was developed using clinical parameters correlated independently with HCO₃⁻ concentration. Diagnostic accuracy of serum total CO₂ and the approximation formula was evaluated by receiver operating characteristic curve analysis and a 2 × 2 table.
RESULTS
Serum total CO₂ correlated strongly with HCO₃⁻ concentration (r = 0.91; P < 0.001). The following approximation formula was obtained by a multiple linear regression analysis: HCO₃⁻ (mmol/L) = total CO₂− 0.5 × albumin − 0.1 × chloride − 0.01 × (estimated glomerular filtration rate + blood glucose) + 15. The areas under the curves of serum total CO₂ and the approximation formula for detection of low bicarbonate and high bicarbonate were 0.981, 0.996, 0.993, and 1.000, respectively. This formula had superior diagnostic accuracy compared with that of serum total CO₂ (86.6% vs. 81.3%).
CONCLUSION
Serum total CO₂ correlated strongly with HCO₃⁻ concentration in pre-dialysis CKD patients. An approximation formula including serum total CO₂ showed superior diagnostic accuracy for low and high bicarbonate compared with serum total CO₂.

Keyword

Acid base balance; Bicarbonates; Carbon dioxide; Chronic kidney disease

MeSH Terms

Acid-Base Equilibrium
Bicarbonates
Carbon Dioxide*
Carbon*
Glomerular Filtration Rate
Humans
Linear Models
Renal Insufficiency, Chronic*
ROC Curve
Bicarbonates
Carbon
Carbon Dioxide