The urine specific gravity dipstick: a useful tool to increase fluid intake in stone forming patients

High fluid intake is the only preventive dietary measure that can be recommended to all patients with stones. However, the efficacy of dietary advice given to patients is unknown. We compared the impact of dietary advice to increase hydration (group 1, 57 patients) and of no dietary advice (group 2, 83 patients) on 24-hour urine volume. No significant difference was noted between groups 1 (1,624 ml.) and 2 (1,732 ml.). We then determined if urine specific gravity dipsticks could help patients increase the 24-hour urine volume. A correlation between 24-hour urine volume and mean urine specific gravity was performed on 263 randomly chosen patients. There was an inverse relationship between urine specific gravity and 24-hour urine volume with a correlation coefficient of 0.522 (y = 1.0207 - 0.00374x). Most patients (81.6%) with 24-hour urine volumes of less than 2.1 had a urine specific gravity of more than 1.010. The use of specific gravity dipsticks was evaluated as a tool to help 24 patients increase the 24-hour urine volume. The 24-hour urine volume increased significantly (p less than 0.05, paired Student's t test) in patients after feedback from specific gravity dipsticks when they were instructed to keep the urine specific gravity at or less than 1.010 (average 24-hour urine volume increased 192%). We conclude that dietary advice may be insufficient to modify fluid intake habits in stone patients. However, modifications of fluid intake habits may be improved by feedback from specific gravity dipsticks.