Nephrology

Renal Tubular Acidosis - Types song

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Renal Tubular Acidosis - Types

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Key points in this song10

RTA is a normal anion gap (hyperchloremic) metabolic acidosis caused by defective renal acid handling, not impaired GFR.
Type 1 (distal) RTA results from failure of alpha-intercalated cells to secrete H⁺ in the collecting duct, causing urine pH that cannot drop below 5.5 even during systemic acidosis.
Type 1 is associated with autoimmune diseases (Sjögren syndrome, SLE), amphotericin B toxicity, and causes hypokalemia with nephrocalcinosis and recurrent kidney stones (calcium phosphate).
Type 2 (proximal) RTA results from defective proximal tubule HCO₃⁻ reabsorption; urine pH is initially alkaline but can drop below 5.5 once serum HCO₃⁻ falls below the reduced threshold.
Type 2 is classically associated with Fanconi syndrome (global proximal tubule dysfunction causing glycosuria, phosphaturia, aminoaciduria), multiple myeloma, and tenofovir or ifosfamide toxicity.
Type 4 RTA results from hypoaldosteronism or aldosterone resistance, impairing both H⁺ and K⁺ secretion in the collecting duct, causing hyperkalemia — the only RTA type with high potassium.
Type 4 is the most common RTA in clinical practice and is classically seen in diabetic nephropathy (hyporeninemic hypoaldosteronism) and use of ACE inhibitors, ARBs, or potassium-sparing diuretics.
The urine anion gap (UAG = urine Na⁺ + K⁺ − Cl⁻) distinguishes renal from GI causes of normal anion gap acidosis; a positive UAG indicates impaired renal NH₄⁺ excretion, pointing to RTA.
Treatment of Type 1 uses oral bicarbonate or citrate; Type 2 requires large bicarbonate doses (worsens bicarbonaturia) plus thiazides; Type 4 is managed by treating the underlying cause and may require fludrocortisone or dietary potassium restriction.
Type 3 RTA is a rare combined proximal and distal defect caused by carbonic anhydrase II deficiency.