VALIDITY OF URINE SPECIFIC GRAVITY WHEN COMPARED WITH PLASMA OSMOLALITY AS A MEASURE OF HYDRATION STATUS IN MALE AND FEMALE NCAA COLLEGIATE ATHLETES

The purpose of this study was to evaluate the response of urine specific gravity (U-sg) and urine osmolality (U-osm) when compared with plasma osmolality (P-osm) from euhydration to 3% dehydration and then a 2-hour rehydration period in male and female collegiate athletes. Fifty-six National Collegiate Athletic Association (NCAA) wrestlers (mean +/- SEM); height 1.75 +/- 0.01 m, age 19.3 +/- 0.2 years, and body mass (BM) 78.1 +/- 1.8 kg and 26 NCAA women's soccer athletes; height 1.64 +/- 0.01 m, age 19.8 +/- 0.3 years, and BM 62.2 +/- 1.2 kg were evaluated. Hydration status was obtained by measuring changes in P-osm, U-osm, U-sg, and BM. Male and female subjects dehydrated to achieve an average BM loss of 2.9 +/- 0.09% and 1.9 +/- 0.03%, respectively. Using the medical diagnostic decision model, the sensitivity of Usg was high in both the hydrated and dehydrated state for males (92%) and females (80%). However, the specificity of U-sg was low in both the hydrated and dehydrated states for males (10 and 6%, respectively) and females (29 and 40%, respectively). No significant correlations were found between U-sg and P-osm during either the hydrated or dehydrated state for males or females. Based on these results, the use of U-sg as a field measure of hydration status in male and female collegiate athletes should be used with caution. Considering that athletes deal with hydration status on a regular basis, the reported low specificity of U-sg suggests that athletes could be incorrectly classified leading to the unnecessary loss of competition.