Distal renal tubular acidosis: pathogenesis and classification.

Distal renal tubular acidosis results from ineffective addition of hydrogen ions to the lumen of the distal nephron. The syndrome is manifested by hyperchloremic metabolic acidosis often associated with hypokalemia. More recently, it has been recognized that hyperkalemia rather than hypokalemia can be a dominant feature of some cases of distal renal tubular acidosis. It has been generally accepted that all cases of this syndrome ultimately resulted from a similar mechanism. The prevailing view was that the abnormality underlying distal renal tubular acidosis was that of inability to either generate or maintain a steep pH gradient across the distal nephron. Recent advances in our understanding of the process of distal acidification have provided evidence that different mechanisms can alter distal hydrogen ion secretion. In this article, the significance of the various indices of urinary acidification and their use in the characterization of the mechanism underlying distal renal tubular acidosis are revised. A classification of distal renal tubular acidosis on the basis of mechanism is presented. The importance of plasma potassium and renal potassium excretion in the evaluation of patients with distal renal tubular acidosis is emphasized.