Adjusted Plasma Chloride and Bicarbonate Concentrations: An Approach to Identifying Acid–Base Disorders

Background Chloride disorders (hypochloremia, hyperchloremia) and bicarbonate disorders (hypobicarbonatemia, hyperbicarbonatemia) are common in clinical medicine and indicate metabolic and/or respiratory acid–base disorders. The normally inverse relationship between chloride and bicarbonate concentrations in the blood is altered, however, by changes in fluid balance, i.e., water excess or deficit, with resulting changes in sodium and other electrolyte concentrations and by anion gap metabolic acidosis, which lowers bicarbonate concentrations but not the chloride concentrations. Methods We used formulas derived over a decade ago that utilize dry slide laboratory technology to adjust plasma chloride and bicarbonate concentrations for changes in water balance, as reflected in changes in plasma sodium concentrations and in the plasma anion gap. We then prospectively validated these formulas in 736 consecutive adults, 499 having abnormal basic metabolic panel results and 237 having normal panel results, using modern wet laboratory technology. Results Plasma chloride and bicarbonate concentrations were inversely correlated (2-tailed P-value <0.0001), but the correlations were only modest (Spearman r: −0.48 for the abnormal group and −0.41 for the normal group). After adjusting the plasma chloride and bicarbonate concentrations using the 2 prior formulas, the inverse correlations were very high, with Spearman r: −0.998 for the abnormal group and −0.999 for the normal group. Conclusions Adjusting plasma chloride and bicarbonate concentrations for any water imbalance and anion gap alterations leads to very high inverse correlations between these 2 anions, allowing accurate assessment of either subtle or overt acid–base disorders.