Urine Anion Gap Calculator
Calculate urine anion gap to assess kidney acid excretion and diagnose metabolic acidosis
Calculate Urine Anion Gap
24-hour urine collection preferred for accuracy
Major cation in urine along with sodium
Major anion in urine, often accompanies ammonium
Example Calculations
Normal Response (Diarrhea)
Urine values: Na⁺ 40 mEq/L, K⁺ 25 mEq/L, Cl⁻ 80 mEq/L
Calculation: 40 + 25 - 80 = -15 mEq/L
Interpretation: Negative UAG indicates high NH₄⁺ excretion (appropriate kidney response)
Renal Tubular Acidosis
Urine values: Na⁺ 60 mEq/L, K⁺ 30 mEq/L, Cl⁻ 45 mEq/L
Calculation: 60 + 30 - 45 = +45 mEq/L
Interpretation: Positive UAG suggests impaired NH₄⁺ excretion (possible RTA)
Reference Ranges
Normal UAG
0 to +10 mEq/L
(Sometimes -10 to +20 mEq/L)
Negative UAG
< 0 mEq/L
High NH₄⁺ excretion
Positive UAG
> +10 mEq/L
Low NH₄⁺ excretion
Clinical Applications
Metabolic Acidosis
Differential diagnosis of non-anion gap metabolic acidosis
Kidney Function
Assessment of renal acid excretion capacity
RTA Diagnosis
Screening for renal tubular acidosis
Ammonium Assessment
Indirect measurement of urinary NH₄⁺
Associated Conditions
Negative UAG
- • Diarrhea
- • Ureterosigmoidostomy
- • Carbonic anhydrase inhibitors
- • Normal kidney response
Positive UAG
- • Type 1 RTA (distal)
- • Type 4 RTA (hyperkalemic)
- • Chronic kidney disease
- • Aldosterone deficiency
Understanding Urine Anion Gap
What is Urine Anion Gap?
The urine anion gap (UAG) is a calculated value that estimates unmeasured ions in urine, primarily ammonium (NH₄⁺). It's used to assess the kidney's ability to excrete acid and helps differentiate causes of metabolic acidosis.
Clinical Significance
- •Differentiates renal vs. non-renal causes of metabolic acidosis
- •Assesses kidney's acid excretion function
- •Screens for renal tubular acidosis
- •Indirectly measures urinary ammonium
Formula & Physiology
UAG = [Na⁺] + [K⁺] - [Cl⁻]