The Effect of Storing Temperature and Duration on Urinary Hydration Markers

The purpose of this investigation was to quantify the effects of storage temperature, duration, and the urinary sediment on urinary hydration markers. Thirty-six human urine samples were analyzed fresh and then the remaining sample was separated into 24 separate vials, six in each of the following four temperatures: 22 °C, 7 °C, -20 °C, and -80 °C. Two of each sample stored in any given temperature, were analyzed after 1, 2, and 7 days either following vortexing or centrifugation. Each urine sample was analyzed for osmolality (UOsm), urine specific gravity (USG), and urine color (UC). UOsm was stable at 22 °C, for 1 day (+5-9 mmol∙kg-1, p > .05) and at 7 °C, UOsm up to 7 days (+8-8 mmol∙kg-1, p > .05). At -20 and -80 °C, UOsm decreased after 1, 2, and 7 days (9-61 mmol∙kg-1, p < .05). Vortexing the sample before analysis further decreased only UOsm in the -20 °C and -80 °C storage. USG remained stable up to 7 days when samples were stored in 22 °C or 7 °C (p > .05) but declined significantly when stored in -20 °C, and -80 °C (p < .001). UC was not stable in any of the storing conditions for 1, 2, and 7 days. In conclusion, these data indicate that urine specimens analyzed for UOsm or USG remained stable in refrigerated (7 °C) environment for up to 7 days, and in room temperature for 1 day. However, freezing (-20 and -80 °C) samples significantly decreased the values of hydration markers.