Urol Res (1995) 23:201-203 9 Springer-Verlag 1995 P. P. Singh - A. K. Pendse 9 A. Ahmed D. V. S. S. Ramavataram - S. K. Rajpurohit A study of recurrent stone formers with special reference to renal tubular acidosis Received: 19 August 1994 / Accepted: 31 March 1995 Abstract Forty-five patients with recurrent renal stone were examined for distal renal tubular acidosis (dRTA) defects by acid challenge test (150mg ammonium chloride/kg body weight). Their 24-h urine samples were analysed for creatinine, calcium, oxalic acid, inor- ganic phosphorus, uric acid, magnesium and citric acid. One-hour urine samples before acid load and hourly samples for the 7 h following acid challenge test were collected and analysed for creatinine, calcium, citric acid, inorganic phosphorus, titratable acidity, and am- monium. The incidence of distal RTA defect was 22.2% in the patients examined. The major biochemical char- acteristics in RTA patients compared with patients without RTA were: (a) significantly higher urinary pH, (b) significantly lower excretion of citric acid, (c) no significant difference in calcium excretion and (d) a tendency toward lower titratable acidity and am- monium excretion. Key words Recurrent stone formers " Renal tubular acidosis In the Indian state of Rajasthan which has a population of over 35000000, recurrent idiopathic urinary tract calcium stone disease is a major health problem [-7, 8, 14, 18J. Although the cause of calcium stone formation is multifactorial and largely unknown, in P. P. Singh (~) 9 A. Ahmed - D. V. S. S. Ramavataram S. K. Rajpurohit Department of Biochemistry, Ravindra Nath Tagore Medical College, Udaipur, Rajasthan, India A. K. Pendse Department of Surgery, RNT Medical College, Udaipur, Rajasthan, India some patients it is due to a defect of distal renal tubular acidification (dRTA). The percentage of such cases can vary widely in different populations. Rampton et at. [17] found it to be present in only 0.1% of stone patients, while Backman et al. [-3] reported an inci- dence of 31%. In an earlier study, we observed it to be present in 24% of cases [1]. This led us to investigate a selected group of recurrent renal tract stone formers for the presence of dRTA. Patients and methods Forty-five radiologically proven renal stone formers admitted to surgical wards or attending the out-patient clinic of the general hospital RNT Medical College Udaipur, were selected for this study. They comprised 42 males (age range 21 58 years) and 3 females (aged 38, 31 and 46 years). All secondary causes of stone formation were excluded. The 24-h urine samples were collected in clean glass bottles containing 10 ml concentrated hydrochloric acid as preser- vative. Fresh urine samples were collected for citric acid analysis and the data were computed on a 24-h basis from 24-h urinary volume. For the acid challenge test, ammonium chloride packed in gelatin capsules was given in a dose of 150 mg/kg body weight to the subjects after a heavy breakfast. The subjects were put on an unre- stricted diet and were ambulatory. Approximately 200 ml water/h was given to the subjects throughout the experiment. A 1-h urine sample was collected prior to the ammonium chloride loading, and thereafter hourly urine samples were collected for 7 h after the acid challenge. The urine samples were collected in clean double-distilled water-washed glass bottles which were immediately corked. The pH was measured by pH meter. Titratable acidity, ammonium, cre- atinine, magnesium, calcium, oxalic acid, inorganic phosphorus and uric acid were analysed in all the samples using standard biochemi- cal procedures. Statistical analysis was carried out using Student's t-test. Results Of the 45 recurrent renal stone formers, 10 (22.2%) were found to have a defect of RTA. These patients could not acidify their urine pH below 5.0 after am- monium chloride loading. The 24-h urine chemistry