Renal tubular acidosis

Type I RTA (distal)
- defect in excretion of acid
- associated with hypergammaglobulinemia, amphotericin B, primary biliary cirrhosis and thyroiditis
- presents with hypokalemia, acidosis and low urinary ammonium production
- inability to lower urine pH below 5.3 despite systemic acidosis
- low urinary citrate and hypercalciuria, causing nephrocalcinosis, renal stone, rickets and osteomalacia (calcium loss and buffering of retained H+ in bone)
- diagnosis: acid load (oral ammonium chloride is given - failure to lower urine pH)
- treatment: oral sodium bicarbonate or citrate

Type II RTA (proximal)
- defect in absorption of bicarbonate
- Fanconi syndrome and osteomalacia occurs
- cardinal features are acidosis, hypokalemia and hypophosphatemia
- apperance of bicarbonate in urine
- urine can be acidified
- expired tetracycline use and Wilson disease is a cause
- diagnosis: IV sodium bicarbonate load (high fractional excretion of bicarbonate)
- treatment: high dose of bicarbonate

Type IV RTA (hyporeninemic hypoaldosteronism)
- commonest RTA
- occurs in diabetes and tubulointerstitial disease
- associated with chronic ingestion of NSAIDs
- cardinal feature is hyperkalemia
- fludrocortisone treatment is effective


Note: osteomalacia can occur in both type I and II
- type III RTA is a rare combination of type I and II