Renal Tubular acidosis

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  • Normal anion gap metabolic acidosis
  • RTA 1: Poor H+ secretion, urinary pH > 5.5  nephrocalcinosis (Ca phosphate)
  • RTA 2: Proximal, failure to reabsorb HCO3 (like acetazolamide), urinary pH < 5.5, Fanconi
  • RTA 4: Aldosterone resistance, hyperkalemia
  • Urine anion gap (UNa - UCl) is positivein RTA

Diagnosis

  • RTA1: Ammonium chloride administration (urinary pH should lower in normal people)
  • RTA2: Bicarbonate administration (urine pH will rise in RTA2)
  • RTA 4: Persistently high UNa despite sodium depleted diet

Treatment

RTA1: Bicarbonate RTA2: Thiazides (enhance HCO3 reabsorption)

Differential diagnosis

Diarrhea (negative Urine Anion Gap: UCl > UNa)