An Aggregate Urine Analysis Tool to Detect Acute Dehydration.

PURPOSE

Urine sampling has previously been evaluated for detecting dehydration in young male athletes. The present study investigated whether urine analysis can serve as a measure of dehydration in men and women of a wide age span. METHODS: Urine sampling and body weight measurement were undertaken before and after recreational physical exercise (median time: 90 minutes) in 57 volunteers aged between 17 and 69 years (mean age: 42). Urine analysis included urine color, osmolality, specific gravity, and creatinine. RESULTS: The volunteers' body weight decreased 1.1% (mean) while they exercised. There were strong correlations between all four urinary markers of dehydration (r = 0.73 to 0.84, P < 0.001). Researchers constructed a composite dehydration index graded from 1 to 6 based on these markers. This index changed from 2.70 before exercising to 3.55 after exercising, which corresponded to dehydration of 1.0% as given by a preliminary reference curve based on seven previous studies in athletes. Men were slightly dehydrated at baseline (mean: 1.9%) compared to women (mean: 0.7%; P < 0.001), while age had no influence on the results. A final reference curve that considered both the present results and the seven previous studies was constructed in which exercise-induced weight loss (x) was predicted by the exponential equation x= 0.20 dehydration index. CONCLUSION: Urine sampling can be used to estimate weight loss due to dehydration in adults up to the age of 70 years. A robust dehydration index based on four indicators reduces the influence of confounders.