Background: Fluid intake is critical for kidney stone prevention. Not all patients are compliant with this recommendation despite its effectiveness.

Objective: To evaluate compliance with fluid intake and urine volume (UV) recommendations in patients with nephrolithiasis and assess factors influencing compliance.

Design: Retrospective study.

Methods: Between 2010 and 2015, first-time kidney stone patients with UV <2.5 L/d on initial 24 hour urine were reviewed. Patients received instruction on strategies to increase fluid intake and target goals of >3 L/d fluid intake and >2.5 L/d UV. Repeat 24 hour urine collections were obtained at 6 and 18 months. Demographic and clinical data were analyzed to determine factors associated with compliance.

Results: 363 patients were included in the study. Mean baseline UV was 1.63 L/d, which increased to 2.5 L/d at 6 months. The compliance rate for UV >2.5 L/d at 6 months was only 50.1%, and decreased to 47.5% at 18 months. Overall, 30 patients (8.3%) had UV <1L/d, and only 20% of these patients reached the target 2.5 L/d at 6 months compared to 50.2% of patients with baseline UV of 1 to 2 L/d, and 61.8% of patients with baseline UV of 2 to 2.5 L/d (P =0.001). Factors associated with increased compliance included male gender (odds ratio [OR], 3.27), surgical procedures for stones (OR 2.3 to 3.5), and baseline UV >1L/d (OR, 3.0). Lower compliance was seen for patients aged >58 years and those with lower urinary tract symptoms (LUTS) (OR, 0.39 and 0.50).

Conclusions: Approximately 50% of first-time stone formers achieve compliance targets for fluid intake and urine volume. Factors decreasing compliance include initial UV <1 L/d, older age, female gender, and the presence of LUTS.

Reviewer’s Comments: When I ask my recurrent stone formers what advice they have been given for stone prevention, I often hear “my doctor only told me to increase fluids.” It occurs to me that patients do not understand the importance of increasing fluid intake and in turn urine volume. Of all the strategies we preach for stone prevention, fluid intake is one of the few that have randomized controlled trial data to support it. It is important to explain that UV is even more important than intake as insensible losses differ from patient to patient; therefore, UV will also differ between patients with the same fluid intake.

The current study assists in understanding which patients are likely to need additional instruction to achieve compliance.In the technology age, there are aides to help patients including apps for mobile devices and attachments for water bottles that flash to remind a patient to drink.

This study also illustrates how as urologists we need to assess and treat patients with LUTS, which can greatly influence compliance with fluid recommendations particularly given the significant impact LUTS have on quality of life.(Reviewer–Nicole L. Miller, MD).