Validity of temperature, duration, and vessel seal on 24-hour urinary hydration markers

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.

Serum and urine osmolality: 8 hours, 24 hours and 1-month sample stability

OBJECTIVES

The body of literature varies significantly regarding serum and urine osmolality stability. Therefore, our aim was to investigate the stability of serum and urine osmolality at different temperatures (room temperature (RT) 4-8 °C, -20 °C) and time conditions (8 h, 24 h, 1 month).

METHODS

The stability study was conducted following the CRESS guidelines, including 40 serum and urine samples. Samples were aliquoted into three aliquots and stored as follows: primary tube stored at RT for 8 h; two capped aliquots stored at 4-8 °C for 8 h and 24 h; one aliquot stored at -20 °C for 1 month. To minimize imprecision error, serum and urine osmolality were measured by the freezing point depression method in triplicate on OSMOMAT 3000 (Gonotech, Germany) analyzer. Percentage difference (PD%) against baseline measurement was calculated. Deviations were assessed against a reference change value of 5.0%.

RESULTS

The PD% for serum and urine osmolality was below 2.0% for all time/temperature conditions. For serum samples: primary tube after 8 h at RT PD% (95% CI) = 0.0% (-0.3, 0.2%); 8 h at 4-8 °C PD% (95% CI) = -0.4% (-0.7, 0.0%); 24 h at 4-8 °C PD% (95% CI) = -0.7% (-0.7, -0.6%); 1 month at -20 °C PD% (95% CI) = -2.1% (-2.4, -1.5%). For urine samples: after 8 h at RT PD% (95% CI) =0.6% (0.2, 0.9%); 8 h at 4-8 °C PD% (95% CI) = -0.2% (-0.5, 0.1%); 24 h at 4-8 °C PD% (95% CI) = -0.2% (-0.5, 0.0%); 1 month at -20 °C PD% (95% CI) = -2.0% (-3.0, -1.0%).

CONCLUSIONS

Changes in osmolality for tested conditions for serum and urine samples, were within acceptance criteria. Reflex and add-on osmolality testing can be performed within the same day in samples kept at RT for 8 h in primary tube and within 24 h, in aliquoted refrigerated samples, without compromising the reliability of test results. For longer storage, samples should be kept at -20 °C.

Short-Term Stability of Urine Electrolytes: Effect of Time and Storage Conditions

The purpose of this investigation was to quantify the effects of storage temperature and duration on the assessment of urine electrolytes. Twenty-one separate human urine specimens were analyzed as baseline and with the remaining specimen separated into eight vials, two in each of the following four temperatures: 22, 7, -20, and -80 °C. Each specimen was analyzed for urine electrolytes (sodium, potassium, and chloride) after 24 and 48 hr. After 24 hr, no significant difference was detected from baseline in urine sodium, potassium, and chloride at all four storage temperatures (p > .05). Similarly, after 48 hr, urine sodium, potassium, and chloride were not significantly different from baseline in all four storage temperatures (p > .05). In conclusion, these data show that urine specimens analyzed for urine sodium, chloride, and potassium are stable up to 48 hr in temperatures ranging from deep freezing to room temperature.