Urine Anion Gap
Detects impaired renal acid excretion during evaluation of non-gap metabolic acidosis.
Urine Anion Gap
-10.0 mEq/L
UAG = (Na + K) − Cl
Interpretation
Negative UAG
Suggests increased NH4+ excretion and an appropriate renal response.
Formula: Urine anion gap = Urine Na⁺ + Urine K⁺ − Urine Cl⁻
A negative UAG traditionally suggests increased urinary ammonium excretion, often seen with gastrointestinal bicarbonate loss such as diarrhea. A positive UAG suggests reduced ammonium excretion and may support renal tubular acidosis in the right setting. Interpretation has limitations, especially in CKD and when unmeasured urinary anions are present.
References
- Battle, D. C., et al. (1982). The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis. New England Journal of Medicine, 307(10), 597-601. https://doi.org/10.1056/NEJM198209023071004
- Goldstein, M. B., et al. (1986). The urine anion gap: A pious hope? American Journal of Nephrology, 6(1), 1-10.
- Kraut, J. A., & Madias, N. E. (2012). Differential Diagnosis of Nongap Metabolic Acidosis. Clinical Journal of the American Society of Nephrology, 7(4), 671-679. https://doi.org/10.2215/CJN.09450911
- Hamm, L. L., et al. (2015). Acid-Base Homeostasis. Clinical Journal of the American Society of Nephrology, 10(12), 2232-2242.
