Validity of Urine Specific Gravity to Determine Hydration Status in NCAA Division I Male and Female Soccer Players

ABSTRACT Introduction Urine specific gravity (USG) is commonly used for rapid determination of hydration status. However, it may not reflect true hydration status when compared to serum osmolality (S osm ). Therefore, the purpose of this study was to assess the agreement between hydration status measured by USG and S osm in National Collegiate Athletic Association (NCAA) Division I soccer players. Methods Sixty-four NCAA Division I soccer players ( n = 31 female) participated in the study. Fasting blood draws occurred in the morning at six timepoints for females and three timepoints for males. Repeated-measures correlations were used to assess relationships between USG and S osm ( α = 0.05). Results Mean S osm was 287.60 ± 4.89 mOsm·kg −1 and mean USG was 1.024 ± 0.006. There was no significant correlation found between S osm and USG in all subjects ( r = −0.06, P = 0.36). Mean S osm in females was 286.54 ± 5.24 mOsm·kg −1 , and mean USG was 1.024 ± 0.006. In females, there was no significant correlation between S osm and USG ( r = −0.12, P = 0.16). Mean S osm in males was 289.35 ± 5.57 mOsm·kg −1 , and mean USG was 1.027 ± 0.031. In males, there was no significant correlation between S osm and USG ( r = 0.11, P = 0.42). Mean S osm in females was significantly lower than in men ( P = 0.04), but no significant differences were found between sexes for USG ( P = 0.09). When assessed for sensitivity, females and males received scores of 78.79% and 83.02%, respectively, whereas the general sensitivity of all subjects was 81.40%. Assessment of specificity revealed that females and males received scores of 19.46% and 28.13%, respectively, whereas the general specificity of all subjects was 20.99%. Conclusion The present study demonstrates a discordance between USG and S osm . Although it lacked specificity in classifying euhydration, USG tended to classify an individual as hypohydrated compared to S osm . Because USG may falsely classify an athlete as hypohydrated, additional measures of hydration status should be taken to avoid overhydration.