Storing urine samples with moisture preserves urine hydration marker stability up to 21 days

Abstract

To assess hydration status, hydration markers [urine color, osmolality, and urine-specific gravity (USG)] are used. Urine color, osmolality, and USG have shown to be stable for 7, 7, and 3days, respectively, at 4°C. However, refrigeration could produce a dry environment which enhances evaporation and potentially affects urine hydration markers. To examine the effect of duration and moisture on urine markers with refrigeration. 24 participants provided urine samples between 9 and 10 AM. Urine color, osmolality, and USG were analyzed within 2h (baseline). Then, each urine sample was divided into two urine cups and placed in a storage container with (moisture condition) and without (no moisture condition) water bath at 3°C. Hydration markers were analyzed at day 1(D1), D2, D7, D10, D14, and D21. A two-way ANOVA (time x condition) and repeated-measures ANOVA on time were performed to examine differences. No significant (p > 0.05) condition x time effect was observed for urine color (p = 0.363), urine osmolality (p = 0.358), and USG (p = 0.248). When urine samples were stored in moisture condition, urine color (p = 0.126) and osmolality (p = 0.053) were stable until D21, while USG was stable until D2 (p = 0.394). When assessing hydration status, it appears that the urine color and osmolality were stable for 21days, while USG was stable for 2days when stored with moisture at 3°C. Our results provide guidelines for practitioners regarding urine storage duration and conditions when urine cannot be analyzed immediately.