Trial Questions Fluid Intake Targets for Preventing Urinary Stone Recurrence

An intervention designed to promote high fluid intake failed to reduce symptomatic stone recurrence in patients with a history of urinary stone disease, a randomized trial showed.

Among over 1,600 participants, symptomatic stone events occurred in 18.6% of those in the intervention group — which included an individualized fluid prescription — versus 19.8% of those in the control group who received guideline-concordant care (HR 0.96, 95% CI 0.77-1.20), reported Charles D. Scales Jr., MD, of the Duke University School of Medicine in Durham, North Carolina, and colleagues in The Lancet.

Of note, 24-hour urine volume increased from baseline in both groups, and was higher in the intervention group at months 6, 12, 18, and 24 compared with the control group.

“The results of the PUSH study do not undermine the importance of increasing fluid intake for stone prevention, as this remains a low-cost, low-risk intervention with likely benefits based on previous literature,” the authors concluded. However, they added, the study indicated that many patients with urinary stone disease and low urine volume will find it difficult to sustain high fluid intake.

Thus, “investigators might need to focus on alternative adherence strategies and secondary prevention strategies that go beyond simply increasing fluid intake,” they suggested.

In a commentary accompanying the study, Kelly Lambert, PhD, of the University of Wollongong in Australia, and Hicham Ibrahim Cheikh Hassan, MD, of the Lebanese American University in Byblos, noted that “the study raises important questions: should guidelines really be recommending unattainable targets that patients are not able to achieve in practice?”

They pointed out that motivation and education may not be enough to reach these hydration targets, and that environmental, occupational, and health system factors need to be considered.

“Framing targets more flexibly with individualized goals that are aligned with work or study patterns, beliefs, access to palatable water, thirst cues, and other competing demands might be more successful,” they wrote. “Coproduction of stone prevention and management guidance with input from patient partners about the realities of daily life with stones is an important next step towards meaningful reductions in recurrence.”

The trial included 1,658 participants (median age 44 years, 57% female) with a history of urinary stone disease and low 24-hour urine volume based on current guidelines, who were enrolled at six academic medical centers in the U.S. between October 2017 and February 2022.

The intervention consisted of a fluid prescription to be consumed from a smart water bottle (additional daily fluid intake in excess of baseline intake required to achieve urine volume of more than 2.5 L per day, as recommended by American Urological Association guidelines), financial incentives to adhere to fluid prescription, health coaching to overcome barriers to consuming more fluids, and patient-selected approaches such as text messaging to maintain increased fluid intake.

Participants in the control group were provided with guideline-concordant recommendations to increase fluid consumption to achieve urinary output of at least 2.5 L per day, in addition to usual stone prevention care.

Looking at secondary findings, urinary storage symptoms of frequency, urgency, and nocturia were greater in the intervention group than the control group at months 6 and 12, but not at other timepoints.

There was no difference in stone growth of at least 2 mm or new stones between groups from baseline to imaging at the end of study, or in the composite outcome of symptomatic stone recurrence, new stone formation, or stone growth of at least 2 mm.

Twelve participants in the intervention group had asymptomatic hyponatremia versus two in the control group, but there were no cases of hyponatremia requiring hospitalization.

Scales and colleagues acknowledged that the study had several limitations. For example, they noted that participants were enrolled from academic medical centers that might treat patients with more severe disease. In addition, they did not control for additional fluid intake not measured by the smart bottle, although they suggested randomization “should balance these unmeasured confounders.”

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