← Clinical Scores and Calculators
Urine Anion Gap
Differentiate renal tubular acidosis (RTA) from GI causes of non-anion gap metabolic acidosis (NAGMA). Estimates unmeasured urinary NH4+.
Indication
- Differentiate renal tubular acidosis (RTA) from GI causes of non-anion gap metabolic acidosis (NAGMA). Estimates unmeasured urinary NH4+.
Criteria
- id: una; label: Urine sodium (mEq/L); type: number; placeholder: e.g. 40
- id: uk; label: Urine potassium (mEq/L); type: number; placeholder: e.g. 30
- id: ucl; label: Urine chloride (mEq/L); type: number; placeholder: e.g. 50
Clinical pearls
- Urine AG is only interpretable in NAGMA and may be falsely positive when urine chloride is <25 mEq/L
- In diarrhea, urine chloride is high and the urine AG is negative
- RTA type 1 (distal): cannot acidify urine (urine pH >5.5)
- RTA type 4: hyperkalemia with NAGMA — most commonly from diabetes and NSAIDs
Source and review
- Batlle DC et al. NEJM 1988; Kamel KS et al. Kidney Int 1990. Last reviewed: 2025-01-01