Use of Corrected Plasmatic Anion Gap for the Diagnosis of Metabolic Acidosis

Abstract

Understanding the acid–base disorders relies on a structured diagnostic approach, based on Henderson-Hasselbalch’s equation. After the diagnosis of metabolic acidosis, the calculation of the plasmatic anion gap (AG) evaluates the excess of unmeasured anions, the reference range being 12 ± 2 mEq/l. However, in case of complex disorders, we need to correct the calculation with some parameters that constitute the true AG. Albumin is most clinically relevant to adjust the calculation of the albumin-corrected anion gap (ACAG), because hypoalbuminemia has an alkalizing effect. ACAG can reduce because of hyperphosphotemia or the increase of some cations (e.g., Ca²⁺, Mg²⁺, and hypergammaglobulinemia). Variations of sodium have to be the same as that of chloride to induce no change in the ACAG. The ratios ΔTAPc/ΔHCO₃^– and Cl/Na are accurate tools to add to the ACAG, which reveal the mechanism of complex acidosis.