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Increasing fluid intake, and thus urinary output, after a kidney stone was associated with fewer recurrences, even when patients did not drink as much as guidelines recommend, a subanalysis of the PUSH trial showed.

In a cohort with lower than optimal urine output, patients who started out above the group average and remained so after a behavioral intervention were about half as likely to experience a recurrent stone as those who stayed below average (P = .0064), after adjustment for other factors.

But patients who increased their daily urine volume by at least 438 mL (about 15 oz) had a 24% lower risk for stone recurrences even when the final volume after intervention fell short of the guideline-based goal. That finding was in a model adjusted for factors including baseline urine volume.

“This is important clinically because you can probably tell that patient who still has ‘low urine volume’ that they probably have helped themselves out in terms of stone recurrence,” said Jonathan Harper, MD, of the University of Washington School of Medicine in Seattle, who presented the results at the American Urological Association (AUA) 2026 Annual Meeting. 

Despite low-certainty evidence for guidelines recommending fluid intake to yield at least 2.5 L of urine output to prevent recurrent kidney stones, “I think most of us would agree high fluid intake is the cornerstone of stone prevention,” Harper said.

Thus, publication of the main trial results in The Lancet in March created controversy, “which was really due to a misinterpretation of the findings,” Harper told attendees at the late-breaking clinical trials session. That study found a behavioral intervention to increase fluid intake for the prevention of recurrent stones boosted urine volume without significantly reducing recurrence over a 2-year period.

“This didn’t tell me that drinking fluid doesn’t work. It just tells me it’s hard to change someone’s behavior,” said Wilson Sui, MD, of the University of Michigan in Ann Arbor, Michigan, who also reported data on stone prevention at the AUA conference but was not involved in the PUSH trial. “What it tells me is that we need to get better ways to help patients adhere.” 

After stone prevention counseling in clinical practice, patients tend to increase their urine by only about 300 mL per day. In Harper’s analysis, the 1461 adults with a symptomatic stone event within the prior 3-5 years started with low urine volume, all less than 2 L per day (average, 1.3 L).

These patients at six US medical centers were randomly assigned to receive usual care or an intervention that included a prescribed goal for fluid intake, financial incentives to encourage adherence, health coaching to overcome hindrances, and strategies such as text message reminders. Average achieved 24-hour urine volume was 1.8 L.

That neither group met the guideline-based goal of 2.5 L “highlights how difficult it is for contemporary patients to meet that urine volume guideline goal,” Harper said. “But in no way do the results undermine the importance of fluid intake.”

Rates of recurrence of symptomatic stones over about 2 years of follow-up were roughly 23% among those who went from low baseline to low achieved urine volume (starting below 1.3 L and ending below 1.8 L), 23% in those who started low and ended above average, 21% in those who stayed steady from above 1.3 L to achieve less than 1.8 L, and 19% in those who started above and ended above average.

The study also examined urine osmolality, the concentration of dissolved solutes in urine. “It’s relatively easy to measure, but it hasn’t been incorporated at least widely into clinical practice for stone disease,” Harper said.

Recurrence of symptomatic stones tracked with quintiles of achieved urine osmolality in a dose-response manner, according to the researchers.

“But at any given urine volume, there’s a wide range of urine osmolalities,” Harper said.

“If urine osmolality is a way to risk-stratify patients for stone recurrence, then it’s another measure that we should be taking into account during our initial evaluation of patients and can perhaps tell us in whom we should be more aggressive about our dietary and metabolic management for stone disease recurrence,” Sui said. “It is an interesting avenue for future research if it bears out because presumably most labs would be able to run a urinary osmolality.”

The trial was funded by the National Institute of Diabetes and Digestive and Kidney Diseases. Harper disclosed having no relevant relationships with industry. 

Sui disclosed relationships with Karl Storz and Boston Scientific. 

Crystal Phend is an award-winning medical journalist with decades of experience reporting on clinical research and healthcare developments across specialties. When not walking the halls at a medical conference, she can be found at a keyboard in upstate New York.