Specific Gravity Test Strips Used in Monitoring Urine Concentrations of Urolithiasis Patients

Abstract

Current therapy for urolithiasis patients includes instructions to increase water intake and 24-hour urine output. Previous studies have measured changes in the 24-hour urine volume to evaluate the efficacy of fluid therapy in each patient. We used paper test strips to monitor urine pH and specific gravity in 22 of our stone clinic patients: 10 were instructed to increase water intake just before the study (group 1) and 12 were not so instructed (group 2). Mean specific gravities of 1.0222 (1.0238 corrected for pH) for group 1 and 1.0197 (1.0220 corrected for pH) for group 2 did not differ significantly.Urine specific gravities also were compared for 3 intervals: 1 to 9 a.m., 9 a.m. to 5 p.m. and 5 p.m. to 1 a.m. Of the 22 patients 10 (3 from group 1 and 7 from group 2) had significant diurnal variations in the urine specific gravities, corrected and uncorrected, among these 3 periods. In addition, both groups had a significantly higher mean specific gravity from 1 to 9 a.m. (1.0234 uncorrected and 1.0248 corrected) than from 9 a.m. to 5 p.m. (1.0194 uncorrected and 1.0218 corrected). The 5 p.m. to 1 a.m. (mean of 1.0220 uncorrected and 1.0239 corrected) specific gravity did not differ significantly in either group.If 1.015 is the highest acceptable specific gravity of urine in stone patients, the findings suggest inadequate dilution of urine in these patients, whether or not they were instructed to increase water intake. Also, the significant diurnal variation in urine specific gravity would allow a nighttime triggering event at these hours of higher urine concentration.