Renal tubular acidosis


  • Class of disorders characterized by impaired reabsorption of filtered bicarbonate or excretion of hydrogen ions
  • Causes hyperchloremic metabolic acidosis, non-anion gap
  • Diagnostic classification starts with low, normal, or high serum potassium
  • Differentiate from uremia in which acidosis is anion gap


Differential Diagnosis


  • ABG or VBG
  • BMP, phos, mag
  • Urine pH
  • Urine electrolytes - Na, K, Cl, Ca, Cr
  • Plasma aldosterone and cortisol for type IV RTA
  • Note that when hyperkalemia is present, aldosterone should be elevated, so a "normal" aldosterone level may be relatively low

Features and Treatment

  • Mild acidosis in adults with bicarb > 20 mEq/L may not require treatment
  • Children should be treated due to impaired growth
  • For type I and II RTA, treat all children and infants
    • Generally, 5-15 mEq/kg/day oral bicarbonate
    • May require IV bicarbonate for severe acidosis
    • PO potassium supplements
    • Treat adults with bicarb < 18-20 mEq/L
    • Treat underlying d/o (Vitamin D, etc.)

Proximal Tubular Acidosis

  • Type II RTA - reduced bicarbonate reabsorption
    • Hypokalemia
    • Serum bicarb 12-20 mEq/L generally
    • Urine pH < 5.5, but can be variable
  • Urine pH > 5.5 if undergoing alkali therapy

Distal Tubular Acidosis

  • Type I RTA - impaired H+ and ammonium secretion
    • Hypokalemia
      • Normokalemia may be seen in chronic interstitial renal disease
    • Serum bicarb may be < 10 mEq/L
    • Urine pH > 5.5
    • Urinary anion gap > 50 mEq/L = Na + K - Cl
    • Nephrolithiasis, calcium stones from chronic acidosis causing bone resorption and hypercalciuria


  • Also distal tubular acidosis
    • Hyperkalemia
    • Mild acidosis, with bicarb generally > 17 mEq/L
    • Urine pH < 5.5
  • Serum aldosterone and cortisol levels to determine between:
    • Adrenal insufficiency, Addison's (low aldosterone, low cortisol)
    • Selective aldosterone deficiency (low aldosterone, normal cortisol)
    • Aldosterone resistance (nl to high aldosterone, nl to high cortisol)