Hyperkalemic hyperchloremic metabolic acidosis in sickle cell hemoglobinopathies

Hyperkalemic distal renal tubular acidosis in salt-losing congenital adrenal hyperplasia

Functional indices of distal urinary acidification were assessed in two male infants, aged 1 and 3 months, with salt-losing congenital adrenal hyperplasia. In both cases the diagnosis was sustained by the presence of elevated plasma levels of 17-hydroxyprogesterone, hyponatremia, hyperkalemia, metabolic acidosis and increased plasma renin activity. Both patients were unable to lower urinary pH below 5.9 either during acute ammonium chloride-induced acidosis or after i.v. administration of furosemide. One patient also failed to decrease urine pH below 5.5 and to increase urinary potassium excretion during sodium sulfate infusion. Oral sodium bicarbonate loading was given to both patients but failed to induce a significant increase in the urine minus blood PCO2 gradient. This gradient remained low also after neutral phosphate administration. Repeated studies after acute administration of fludrocortisone in one case or after prolonged administration of hydrocortisone in the other resulted in complete normalization of all functional studies. We conclude that salt-losing congenital adrenal hyperplasia can lead to hyperkalemic distal renal tubular acidosis in early infancy. The defective renal secretion of hydrogen ion and potassium is probably related to the abolishment of the negative potential difference in the cortical collecting tubule induced by the impaired reabsorption of sodium.

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.