Renal tubular acidosis


  • Type I (distal H+ secretion defect): low serum K+, urine pH >5.5, associated with autoimmune disease, hypercalcemia
  • Type II (proximal HCO3- reabosrbtion defect): low serum K+, urine pH < 5.5, associated with multiple myeloma, drugs (eg, sulfa)
  • Type III (rare): normal serum K+, urine pH < 5.5, associated with renal insufficiency
  • Type IV (hyporeninemic hypoaldosteronism): high serum K+, urine pH < 5.5, associated with diabetes mellitus, drugs (eg, NSAIDs)


Other causes of normal gap metabolic acidosis

  • Gastrointestinal loss of HCO3-, eg, diarrhea, pancreatic ileostomy or ileal loop bladder
  • Renal tubular acidosis
  • Recovery from diabetic ketoacidosis
  • Dilutional acidosis from rapid administration of 0.9% NaCl
  • Carbonic anhydrase inhibitors
  • Chloride retention or administration of HCl equivalent or NH4Cl

See related DDx

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