Poor compliance of recurrent stone formers to increase their fluid intake in spite of repeated recommendation

ABSTRACT Background The aim of this study was to evaluate 24-h urine volume (UV), estimated osmolarity (eUosm), and Tiselius APCaOx index (TIS) in 181 calcium oxalate stone formers, and the changes achieved in response to the recommendation to reach a UV of at least 2 l per day, during a follow-up of at least 3 years. Methods Patients of each sex were a posteriori divided into recurrent (R) and non-recurrent (NR) stone formers according to stone events during follow-up. UV, eUosm, and TIS were evaluated at baseline (BSL) and End (END). TIS was also determined in first morning urine. Results were compared by two-way ANOVA or chi square. Results Mean follow-up was 6.8 years. The 24-h osmolar excretion did not differ between R and NR in either sex, and remained stable between BSL and END. UV was significantly lower in R than NR, both at BSL and END, and eUosm was 100–150 mosm/kg H2O higher in R. In both sexes, the increase in UV observed between BSL and END was significantly smaller in R than NR. TIS values were significantly higher in R than NR. They were higher at END than at BSL only in R patients, suggesting a poor compliance of R to drink more. The threshold of TIS for a high risk of crystalluria was found to be 2.45 in both men and women. Conclusion In conclusion, the patients who showed recurrence of lithiasis not only had lower baseline UV, but were also less able to increase UV than those who did not recur, in spite of recommendations to drink more. Based on preliminary information in the literature, a clinical trial could be designed to evaluate, in these patients, if a low dose of a selective V2 receptor antagonist, increasing their diuresis (and thirst), would prevent new stones.