DISTAL RENAL TUBULAR-ACIDOSIS - RECENT ADVANCES

Tubular acidosis is diagnosed when hyperchloremic acidosis is associated with inappropriate NH4 excretion (less-than-or-equal-to 40 mmol/24 hours). Urinary pH is variable because it depends on the secretion of H+ into the collecting duct and is inversely correlated with the amount of ammonia available in the urine. Administration of NaHCO3 for diagnostic purpose allows to eliminate proximal tubular acidosis and to measure the elevation of urinary PCO2 reflecting the secretion of H+ in the collecting duct. Hypokalemia points towards distal tubular acidosis, either by defect of H+-ATPases pumps, or by the incapacity to create a normal gradient of H+. In contrast hyperkalemia suggests distal tubular acidosis associated either with hypoaldosteronism or with diminution of trans-epithelial voltage or with pseudohypoaldosteronism. The incidence of distal tubular acidosis with hyperkalemia is increasing whereas distal tubular acidoses with hypokalemia remain rare.