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. Ammonia (not excreted in Renal Tubular Acidosis)
  2. Sulfates
  3. Phosphates
  4. Bicarbonates
  5. Organic anions
    1. Lactate
    2. Citrate
  • Labs
  1. Urine Anion Gap (obtain urine Electrolytes)
    1. Urine Anion Gap = Urine Sodium + Urine Potassium - Urine Chloride
  • Interpretation
  1. Normal: UAG = -10 to +10
  2. Decreased Urine Anion Gap <-10
    1. Extrarenal (e.g. Diarrhea, TPN) Non-Anion Gap Metabolic Acidosis
    2. Gastrointestinal bicarbonate losses (e.g. Diarrhea, TPN)
    3. Appropriate renal ammonia excretion
  3. Increased Urine Anion Gap >+10
    1. Renal Non-Anion Gap Metabolic Acidosis
    2. Impaired renal ammonia excretion
    3. See Renal Tubular Acidosis