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Urine Sodium Na Urine Potassium K Urine Chloride Cl Urine Anion Gap Explanation and Clinical Context The urine anion gap is a practical bedside calculation that estimates urinary ammonium excretion. It is calculated using the sum of urine sodium and urine potassium minus urine chloride. Ammonium is excreted in association with chloride therefore low chloride relative to sodium and potassium suggests impaired ammonium excretion.
A positive urine anion gap indicates low ammonium excretion which is characteristic of renal tubular acidosis type one or type four. A negative urine anion gap reflects increased ammonium excretion which is commonly seen in metabolic acidosis due to extrarenal bicarbonate loss such as in diarrhea. This interpretation helps clinicians differentiate renal from extrarenal causes of metabolic acidosis and guides appropriate therapeutic decisions.
Reference Kraut J and Madias N. Evaluation of acid base disorders. Clinical Journal of the American Society of Nephrology.
2010.
Evidence & references1 primary source mapped
- Source 1
Batlle DC, Hizon M, Cohen E, Gutterman C, Gupta R. The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis. N Engl J Med. 1988;318(10):594–599. doi:10.1056/NEJM198803103181002. Open source
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