We define the role of urine volume as a stone risk factor in idiopathic calcium stone disease and test the actual preventive effectiveness of a high water intake.

We studied 101 controls and 199 patients from the first idiopathic calcium stone episode. After a baseline study period the stone formers were divided by randomization into 2 groups (1 and 2) and they were followed prospectively for 5 years. Followup in group 1 only involved a high intake of water without any dietetic change, while followup in group 2 did not involve any treatment. Each year clinical, laboratory and radiological evaluation was obtained to determine urinary stone risk profile (including relative supersaturations of calcium oxalate, brushite and uric acid by Equil 2), recurrence rate and mean time to relapse.

The original urine volume was lower in male and female stone formers compared to controls (men with calcium oxalate stones 1,057 plus/minus 238 ml./24 hours versus normal men 1,401 plus/minus 562 ml./24 hours, p less than 0.0001 and women calcium oxalate stones 990 plus/minus 230 ml./24 hours versus normal women 1,239 plus/minus 440 ml./24 hours, p less than 0.0001). During followup recurrences were noted within 5 years in 12 of 99 group 1 patients and in 27 of 100 group 2 patients (p = 0.008). The average interval for recurrences was 38.7 plus/minus 13.2 months in group 1 and 25.1 plus/minus 16.4 months in group 2 (p = 0.016). The relative supersaturations for calcium oxalate, brushite and uric acid were much greater in baseline urine of the stone patients in both groups compared to controls. During followup, baseline values decreased sharply only in group 1. Finally the baseline urine in patients with recurrences was characterized by a higher calcium excretion compared to urine of the patients without recurrences in both groups.

We conclude that urine volume is a real stone risk factor in nephrolithiasis and that a large intake of water is the initial therapy for prevention of stone recurrences. In cases of hypercalciuria it is suitable to prescribe adjuvant specific diets or drug therapy.