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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.

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