Renal Tubular Acidosis Explained

Kidney Tubules AnatomyI hate really hate studying this material but once you understand it, it becomes very easy to memorize.

Remember in renal tubular acidosis (RTA) there is normal anion gap.  [Na – (Cl – HCO3)] = 6-12.
Proximal part is the upper part of the renal tubules, while the distal part is the end part of the tubules.
Type II (Proximal)

  1. Pathophysiology: Decreased ability of the proximal kidney tubules to reabsorb most of the filtered bicarbonate because normally bicarbonate is filtered at the proximal tube.
  2. Urine pH: Variable: Urine pH is basic until bicarbonate is depleted, the it is acidic (less than 5.5)
  3. Blood K+ level: Low
  4. Kidney Stones: No
  5. Associations
    • Diagnosis: Infuse bicarbonate and evaluate the urine pH
    • Treatment: Thiazide because it causes volume depletion, which will enhance bicarbonate reabsorption.

    Type I (Distal)

    1. Pathophysiology: Distal tubule is damaged so it is unable to generate bicarbonate. Without bicarbonate, H+ cannot be secreted in the tubule to the urine, raising urine pH.
    2. Urine pH: Urine pH more than 5.5.
    3. Blood K+ Level: Low
    4. Kidney Stones: Yes
    5. Associations
      • Amphotericin use
      • Lithium Use
      • Sickle Cell Disease
      • Autoimmune Diseases (SLE, Sjorgen Syndrome, Rheumatoid Arthritis, etc)
    6. Diagnosis: Infuse acid
    7. Treatment: Bicarbonate to be absorbed in the proximal tubule, because majority of the bicarbonate is absorbed there.

    Type IV (Distal)

    1. Pathophysiology: Decreased or diminished effect of aldosterone at the kidney tubule. Loss of sodium and retention of potassium and hydrogen ions.
    2. Urine pH: Less than 5.5
    3. Blood K+ level: High
    4. Kidney Stones: No
    5. Associations
      • Diabetes
      • Addison’s Disease
      • NSAIDs
    6. Diagnosis: Urine salt loss, despite sodium restricted diet
    7. Treatment: Fludrocortisone