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

Introduction 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 3 days, respectively, at 4 °C. However, refrigeration could produce a dry environment which enhances evaporation and potentially affects urine hydration markers. Purpose To examine the effect of duration and moisture on urine markers with refrigeration. Methods 24 participants provided urine samples between 9 and 10 AM. Urine color, osmolality, and USG were analyzed within 2 h (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. Results 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). Conclusion When assessing hydration status, it appears that the urine color and osmolality were stable for 21 days, while USG was stable for 2 days 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.