Urine anion gap can differentiate respiratory alkalosis from metabolic acidosis in the absence of blood gas results

Abstract

Introduction: Low plasma bicarbonate concentration due to chronic respiratory alkalosis may be misdiagnosed as metabolic acidosis and mistreated with administration of alkali therapy, particularly when arterial blood gas is not available. Methods:We measured urine anion gap [urine (Na + + K + ) -(Cl − )], as a surrogate of renal ammonium excretion in 15 patients presenting with hyperventilation and low serum bicarbonate concentration to distinguish chronic respiratory alkalosis (CRA) from metabolic acidosis (MA) when blood gas was unavailable.Results: Hyperventilation and low serum bicarbonate concentrations were associated with urine pH above 5.5 and positive urine anion gap in all, suggesting CRA. The diagnosis was later confirmed by obtaining capillary blood gas, which showed a decrease in PCO 2 and high normal pH values. Conclusion:The use of urine anion gap can help to differentiate between chronic respiratory alkalosis and metabolic acidosis, especially when arterial blood gas is not obtained.