Patients in the hydration group were also given reusable drinking containers and 20 vouchers per month redeemable for 1.5 L of bottled water, investigators reported.
Urine volume did significantly increase in the hydration group versus controls, by 0.6 L per day (P less than .001). However, change in eGFR – the primary outcome – was not significantly different between groups. Mean change in eGFR was –2.2 mL/min per 1.73 m2 in patients coached to drink more water and –1.9 mL/min per 1.73 m2 in those coached to maintain water intake (P = .74).
Some secondary outcome measures demonstrated significant differences in favor of the hydration group. Plasma copeptin and creatinine clearance both showed significant differences in favor of the hydration group. In contrast, there were no significant differences between intervention arms in urine albumin or quality of health, according to analyses of secondary outcomes described in the study report.
There are several ways to interpret the finding that drinking more water had no effect on eGFR, investigators said. Increasing water intake may simply not be protective against kidney function decline. Perhaps follow-up longer than 1 year would be needed to see an effect, or perhaps there was an effect, but the study was underpowered to detect it.