Normal anion gap metabolic acidosis

Differential Diagnosis

• Mild AKI, causing decreased ammonia excretion
• Lower GI diarrhea
• Fistulas
  • Pancreatic
  • Ileocutaneous
• Carbonic anhydrase inhibitors
• Renal tubular acidosis (RTA)
  • Type 1 (hypokalemic distal)
  • Type 2 (proximal)
  • Type 4 (hyperkalemic distal)
• Ureteral diversion (e.g. ileal loop)
• Iatrogenic
  • Dilution acidosis

Investigations

• Serum electrolytes showing normal anion gap metabolic acidosis
• Urine anion gap (UNa + UK – UCl)
  • Difference between unmeasured anions (i.e. NH4^+^) and unmeasured cations
    • For most patients, approximates ammonium excretion
  • If negative, suggests presence of ammonium (appropriate)
  • If kidneys are responding properly, the UAG should be negative
  • If defect in acid excretion, UAG should be positive
• Urine pH