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Harvard Medical School. Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study.

Created: 4/7/2006
Updated: 4/7/2006


Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study.
Borghi L, Meschi T, Amato F, Briganti A, Novarini A, Giannini A.
J Urol. 1996 Mar;155(3):839-43.


  • Increasing urine volume to prevent stone recurrences has been in use since the time of Hipprocrates
  • Increase in urine volume should decrease the concentration of calcium, oxalate, phosphate and uric acid with subsequent reduction in the saturation of some of the salts that form stones
  • No studies with appropriate methodology on the protective effect of high urine volume exist (Limiting issues of previous studies include absence of a control group, concomitant cofactors such as diet changes, limited number of subjects, and too short a follow-up period)
  • Also, has not been established whether idiopathic calcium stone formers have a reduced baseline urine volume compared to healthy subjects not forming stones
  • The current study quantifies urine volume for idiopathic calcium stone formers, and assesses the effect of high water intake (without diet changes) in preventing recurrences. It also attempts to identify any biochemical urine factors to predict recurrences

Materials and Methods

  • 101 control patients and 199 stone patients from their 1st idiopathic stone episode were studied from 1986
  • Control patients were identified in the same geographical area and matched for age, sex, weight and working activity
  • 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
  • Follow-up in group 1 only involved a high intake of water greater or equal to 2l/day) without any dietetic change, while follow-up in group 2 did not involve any treatment
  • Annual 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 +/- 238 ml./24 hours versus normal men 1,401 +/- 562 ml./24 hours, p < 0.0001 and women calcium oxalate stones 990 +/- 230 ml./24 hours versus normal women 1,239 +/- 440 ml./24 hours, p < 0.001)
  • During follow-up 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 +/- 13.2 months in group 1 and 25.1 +/- 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 follow-up, baseline values decreased sharply only in group 1
  • Baseline urine in patients with recurrences was characterized by a higher calcium excretion compared to urine of the patients without recurrences in both groups


  • Patients with idiopathic calcium stones have a urine volume at the 1st episode that is lower than the volume of healthy control subjects
  • Simple increase in water intake, without changes in diet, can prevent recurrences
  • The number of recurrences in the untreated stone formers was significantly greater over 5 years and the interval to before onset of recurrence was shorter, compared to the treated stone formers. These data indicate the protective role of a high water intake after the 1st stone idiopathic calcium stone episode
  • Relative supersaturation levels for calcium oxalate and brushite was double that of controls indicating a strong tendency for calcium stone formation
  • A considerable decrease in supersaturation values was observed in the treated stone former group compared to the untreated stone formers probably representing the chemical basis for the lower recurrence rate (similar picture was seen with supersaturation values of uric acid)
  • The only urine factor which could predict recurrence was baseline urinary calcium levels which were greater in those patients who had recurrence compared to those who did not


  • Urine volume in patients with idiopathic calcium stones is lower than normal subjects
  • Adequate water intake may exert a protective effect against recurrences
  • High water intake reduces the saturation of stone forming salts
  • In cases of hypercalciuria it is suitable to prescribe adjuvant specific diets or drug therapy

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