Urine Anion Gap Calculation
Urine anion gap (UAG) is calculated as the difference between principal urinary cations (sodium and potassium) and principal urinary anion (chloride). [1]
Calculation Formula
- UAG = (Urine sodium + Urine potassium) − Urine chloride. [1]
Units and Measurement Requirements
- UAG should be calculated using concentrations in mEq/L (equivalently mmol/L for these ions) from urine electrolyte measurements. [1]
Practical Example
- If UNa = 40 mEq/L, UK = 20 mEq/L, and UCl = 30 mEq/L, then UAG = (40 + 20) − 30 = 30 mEq/L. [1]
Interpretation Relevance
- UAG is used as an estimate of the net urinary excretion of non-chloride anions versus ammonium handling in metabolic acidosis evaluation when direct urine ammonium measurement is not available. [1]
Common Calculation Pitfalls
- Excluding potassium from the UAG formula changes the computed value because potassium contributes to the principal urinary cations used in the standard UAG calculation. [1]
- Mixing units across UNa, UK, and UCl invalidates the arithmetic because UAG depends on consistent concentration units. [1]