Sodium Restriction as Initial Conservative Treatment for Urinary Stone Disease

Abstract

Sodium restriction is widely recommended to prevent urinary stone recurrence. However, the effect of urinary sodium excretion has not been fully evaluated. We investigated the relationship between urinary sodium, urinary metabolite excretion and the risk of recurrence in urinary stone formers. Selected for study were 798 stone formers with no evidence of metabolic disorders as the cause of abnormal urinary solutes. We analyzed the relationship between urinary sodium and other metabolic parameters by gender. Values were adjusted by covariates according to correlation status. Patients were divided into stone formers with hypernatriuresis or normal natriuresis (less than 220 mEq daily) and urinary parameters were compared. Kaplan-Meier analysis was done to determine the cumulative incidence of recurrent stones by urinary sodium. Patients were considered recurrence-free at a minimum followup of 3 years without incidence. In the 492 men and 306 women mean ± SD age was 40.0 ± 11.4 and 45.4 ± 12.7 years, and mean body mass index was 23.9 ± 3.1 and 23.0 ± 3.0 kg/m(2), respectively. Using covariate adjusted partial correlation coefficients urinary sodium was noted to influence volume, pH, calcium, uric acid, oxalate and citrate in men, and volume, pH, calcium, uric acid and citrate in women (each p <0.05). At a median followup of 56.1 months 46 of 98 stone formers (46.9%) with normal natriuresis experienced stone recurrence vs 60 of 93 (64.5%) with hypernatriuresis. Patients with hypernatriuresis also had significantly decreased time to recurrence than those with normal natriuresis (log rank test p = 0.043). Results show that urinary sodium is an important determinant of other stone forming parameters and of the risk of recurrent stones. These findings suggest that a sodium restricted diet should be the initial step when treating stone formers.