Determination of serum bicarbonate (HCO3 - ) using arterial blood gas analysis in patients with diabetic ketoacidosis allows for the evaluation of the severity of the condition, determines whether HCO3 - therapy is required, and tracks the progression and resolution of the disease. Serum carbon dioxide combining power (CO2CP) from venous chemistry analysis has often been used as an indicator of metabolic acidosis. This study investigated the relationship between HCO3 - and CO2CP and developed an approximation formula for serum bicarbonate concentration using its predictor variables, as this may lessen the need to repeat arterial blood gas analysis or be used in settings in which blood gas analyzers are unavailable.

This single-center, retrospective, cross-sectional study investigated a total of 77 patients diagnosed with diabetic ketoacidosis. Assessment of the bivariate correlations between serum HCO3 - and serum CO2CP as well as other potential predictor variables was done via Pearson’s correlation coefficient. Predictor variables that were significantly correlated with serum HCO3 - were identified and an approximation formula was developed by regression analysis. Evaluation of the correlation between the approximated HCO3 - value and the actual serum HCO3 - concentration was performed using correlation coefficient and residual statistics to assess agreement.

Serum CO2CP had significant correlation with serum HCO3 - (r = 0.768, p < 0.05). By multiple regression analysis, the following approximation formula was therefore expressed: HCO3 - = 12.682 + (0.612 x CO2CP) – [ketones] + (0.085 x BUN) - (0.026 x SGPT) – (1.23 x Creatinine) - (0.067 x Chloride). Examination of residuals revealed a mean of zero (0), indicating no significant difference between the actual and approximated levels of serum HCO3 -

The predictor variables included in the formula collectively contribute significantly to the approximation of serum HCO3 - . The approximated serum HCO3 - values also showed significant correlation with actual serum HCO3 - concentration; thus, the formula may be utilized to derive an approximation of serum bicarbonate concentration in patients with diabetic ketoacidosis.