Evaluation of physiological measures for correcting variation in urinary output: Implications for assessing environmental chemical exposure in children

Effect of Seasonal Temperature and Humidity on Urine Density in Children

“…As Usg is known to be higher in dehydration, dehydration was an exclusion criteria for children being evaluated in this study making it different from our study. 9 In the current study a significantly higher urine density was found in summer and spring compared to autumn and winter. Increase in temperatures was parallel with increase in urine density in hot seasons indicating the importance of hydration similar to our study.…”

Urine-sampling methods for environmental chemicals in infants and young children

“…Creatinine adjustment to account for dilution may not be appropriate for some chemicals in young children (or pregnant women) and creatinine-adjusted metabolite concentrations should never be compared among individuals of vastly different age groups (i.e., children versus adults) (Fenske et al, 2005;Pearson et al, 2009). Creatinine excretion during the newborn period is reportedly higher and more variable compared with later infancy (Dorey and Zimmermann, 2008) and the limitations of standardizing urinary excretion of solutes during this period has been previously documented (Matos et al, 1999).…”

“…In some cases, specific gravity assessments may be a more robust measure to correct for urinary output as it introduces less variability (appears to be independent of age and seasonal variation) and is very easily analyzed using a handheld refractometer (Pearson et al, 2009). Specific gravity is the ratio of the density of the urine to that of water and is affected by the number and weight of solute particles (urea, chloride, sodium, potassium, phosphate, uric acid, and sulfate) and on the temperature of the sample, in contrast to urine osmolality which depends solely on the number of solute particles (Pradella et al, 1988).…”

“…Specific gravity is the ratio of the density of the urine to that of water and is affected by the number and weight of solute particles (urea, chloride, sodium, potassium, phosphate, uric acid, and sulfate) and on the temperature of the sample, in contrast to urine osmolality which depends solely on the number of solute particles (Pradella et al, 1988). Specific gravity may not be appropriate for study participants with certain conditions (e.g., diabetes and nephrotic syndrome (Voinescu et al, 2002)) where heavy molecules such as glucose and protein may disproportionately increase the measurement (Pearson et al, 2009) resulting in an underestimate of the urine analyte concentration. Good correlations (r ¼ 0.933) have been observed between urine specific gravity and osmolality in neonates (Leech and Penney, 1987).…”

“…The robustness of both the creatinine and specific gravity readings to freeze-thaw cycles (Anestis et al, 2009;Pearson et al, 2009) and to temperature fluctuations has been debated (Alessio et al, 1985;Riboli et al, 1995). Urine specific gravity does appear to be more stable than creatinine over storage temperatures ranging from À20 to 931C (Cook et al, 2007).…”