Urine acidification capacity in renal stone formers.

A short ammonium chloride loading test was used in the investigation of renal acidification capacity of 51 patients with idiopathic recurrent renal stones containing calcium. Many of these patients had suffered from prolonged and severe stone disease. In 31% of the patients an impaired acidification with varying degrees of severity was found. Eight patients had defects suggesting distal renal tubular acidosis (RTA). One case with the complete and two cases with the incomplete form of RTA were found. A further five patients, who were all able to acidify their urine to an acid pH, had milder defects in the excretion of titratable acid and/or ammonium ions which may indicate an early stage of distal tubular acidosis. Six patients were suspected of having a proximal acidification defect, as they showed delayed responses to the ammonium chloride induced acidosis.