Lab

Urinary Anion Gap

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Urinary Anion Gap, Urine Anion Gap

  • Indications
  1. Non-Anion Gap Metabolic Acidosis
  2. Distinguishes renal from extra-renal causes
  • Physiology
  • Measures unmeasured anions present in urine
  1. Ammonium (not excreted in Renal Tubular Acidosis)
  2. Sulfates
  3. Phosphates
  4. Bicarbonates
  5. Organic anions
    1. Lactate
    2. Citrate
  • Calculation
  1. UAG = Urine Sodium + Urine Potassium - Urine Chloride
  • Interpretation
  • Normal
  1. UAG = -10 to +10
  • Interpretation
  • Abnormal
  1. Decreased Urine Anion Gap <-10
    1. Extrarenal Non-Anion Gap Metabolic Acidosis (e.g. gastrointestinal bicarbonate losses)
  2. Increased Urine Anion Gap >+10
    1. Renal Non-Anion Gap Metabolic Acidosis (Urine pH will also be >6.0)
    2. Causes
      1. Type 1 Renal Tubular Acidosis
      2. Type 4 Renal Tubular Acidosis (Hypoaldosteronism)
      3. Renal Failure