Urinary Anion Gap

Aka: Urinary Anion Gap, Urine Anion Gap

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II. Indications

  1. Non-Anion Gap Metabolic Acidosis
  2. Distinguishes renal from extra-renal causes

III. 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

IV. Calculation

  1. UAG = Urine Sodium + Urine Potassium - Urine Chloride

V. Interpretation: Normal

  1. UAG = -10 to +10

VI. 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

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