Study Type – Therapy (cost‐effectiveness meeting)Level of Evidence 2bWhat's known on the subject? and What does the study add?One of the major problems with nephrolithiasis is the high rate of recurrence, which can effect up to 50% of patients over a 5‐year period. Patients with recurrent stones are recommended to increase fluid intake based on prospective studies that show a reduction in recurrence rates in patients who intake a high volume of water. Strategies to reduce stones in recurrent stone formers are quite effective with a >50% risk reduction with increased fluid intake alone. Unfortunately, despite a high societal cost and morbidity, there are no prospective studies evaluating the benefit of fluid intake to prevent stone disease in subjects without a prior history of stone but at risk for stones.The budget impact analyses show that prevention of nephrolithiasis can have a significant cost savings for a payer in a healthcare system and reduce the stone burden significantly. Future studies will need to assess the feasibility and effectiveness of such an approach in a population.OBJECTIVE To evaluate the impact of primary prevention of stones using a strategy of increased fluid intake. SUBJECTS AND METHODS A Markov model was constructed and analysed using Excel to calculate and compare the costs and outcomes for a virtual cohort of subjects with low vs high water intake. A literature search was used to formulate assumptions for the model including an annual incidence of urolithiasis of 0.032%, annual risk of stone recurrence of 14.4% and 40% risk reduction in subjects with high water intake. Costs were based on resource utilisation from the Delphi panel and official price lists in France. Outcomes were based on payer perspective and included direct and indirect costs and loss of work. RESULTS The base‐case analysis found total cost of urolithiasis is €4267 with direct costs of €2767, including cost of treatment and complications. The annual budget impact for stone disease based on 65 million inhabitants is €590 million for the payer. The use of high water intake by 100% of the population results in annual cost savings of €273 million and 9265 fewer stones. Even if only 25% of the population is compliant, there is still a cost saving of €68 million and 2316 stones. The model was evaluated to determine the impact of varying the assumptions by ±10%. For example, when the incidence of stone disease is increased or decreased by 10% then the mean (range) baseline cost will change by €59 (531–649) million for the payer and savings will either increase or decrease by €27 (246–300) million. The largest impact on cost savings occurs when varying risk reduction of water by 10% resulting in either a mean (range) increase or decrease by €35 (238–308) million. Varying cost of stone management by 10% has an impact of ±€17 million. Varying other factors such as stone recurrence by 10% has only an impact of ±€9 million and varying risk of chronic kidney disease ±€1 million, as they affect only a portion of the population. CONCLUSIONS The budget impact analyses show that prevention of nephrolithiasis can have a significant cost savings for a payer in a healthcare system and reduce the stone burden significantly. Future studies will need to assess the feasibility and effectiveness of such an approach in a population.

Preventing recurrent urolithiasis has a significant cost savings potential for a payer as a result of a reduced stone burden. However, compliance is an important factor in determining cost-effectiveness.

Preventing dehydration in subjects at risk may provide a means of primary prevention of kidney stones. The purpose of this pilot study was to assess the hydration status of an at-risk group of steel plant workers based on end-of-shift ('post-shift') spot urine osmolality and 24-h urinary stone risk parameters. 100 volunteers were recruited from Gerdau Midlothian steel mill in Texas on 11/14/14 and 12/5/14. Clinical data were recorded and post-shift spot urine sample was used to measure urine osmolality. Participants were invited to submit a 24-h urine sample within 4 weeks of enrollment. The mean age was 41 years and 95 % were men. The majority of subjects were white (75 %), followed by 10 % Hispanic and 9 % black. The mean body mass index was 30.1 kg/m and overall 16 % had a past history of stone disease. Mean post-shift urine spot osmolality was 704.5 mOsm (169-1165 mOsm) and was >800 and >700 mOsm in 39 and 57 %, respectively. Among 59 24-h urines samples, the mean volume was 1.89 ± 0.92 l/day, with 56 % < 2 L and 17 % < 1 L. Elevated levels of urinary analytes were found in 29 % of subjects for calcium (>250 mg/TV), 39 % for uric acid (>700 mg/TV), 25 % for oxalate (>45 mg/TV) and 50 % for sodium (>200 meq/TV). The prevalence of stone disease in this population of steel workers was higher than the published prevalence of stone disease in the general population. A significant number of workers had concentrated post-shift and 24-h urines and elevated levels of urinary analytes.

The association between fluid intake and bladder cancer risk remains controversial. Very little is known about to which extent the amount of water intake influences the action of excreting toxics upon the urinary system. This proof of concept trial investigates the effect of water intake on mutagenesis in smokers, a high risk population for bladder cancer. Methods. Monocentric randomized controlled trial. Inclusion Criteria. Male subjects aged 2045–45 y/o, smokers, and small drinkers (24-hour urinary volume <1 L and osmolality >700 mOsmol/kg). Outcomes. 4-ABP DNA adducts formation in exfoliated bladder cells in 24-hour urine collection and urinary mutagenicity in 24-hour urine. Test Group. Subjects consumed 1.5 L daily of the study product (EVIAN) on top of their usual water intake for 50 days. Control Group. Subjects continued their usual lifestyle habits. Results. 65 subjects were randomized. Mean age was 30 y/o and mean cigarettes per day were 20. A slight decrease in adducts formation was observed between baseline and last visit but no statistically significant difference was demonstrated between the groups. Urinary mutagenicity significantly decreased. The study shows that increasing water intake decreases urinary mutagenicity. It is not confirmed by urinary adducts formation. Further research would be necessary.