Primary distal renal tubular acidosis as a result of a gradient defect

It has been generally accepted that primary distal renal tubular acidosis (DRTA) is the result of a defect in proton secretion in the distal nephron (secretory defect). We report an infant with DRTA, evidenced by spontaneous hyperchloremic metabolic acidosis with low urinary ammonium excretion rate and inability to decrease urine pH during acidosis, who nevertheless exhibited an intact ability to increase urinary carbon dioxide partial pressure (pCO2) during maximal urine alkalinization and normal ability to acidify the urine after furosemide, suggestive of a gradient-type defect DRTA. This patient had never been exposed to amphotericin B. To our knowledge, this is the first fully documented report of primary DRTA that can be attributed to gradient defect.