Accuracy of urine specific gravity and osmolality as indicators of hydration status

reduce the adverse consequences of exertion-related and acute intentional dehydration research has focused on monitoring hydration status. This investigation: 1) compared sensitivity of urine specific gravity (U-sg), urine osmolality (U-osm) and a criterion measurement of hydration, plasma osmolality (P-osm), at progressive stages of acute hypertonic dehydration and 2) using a medical decision model, determined whether U-sg or U-osm accurately reflected hydration status compared to P-osm among 51 subjects tested throughout the day. Incremental changes in P-osm were observed as subjects dehydrated by 5% of body weight and rehydrated while U-sg and U-osm showed delayed dehydration-related changes. Using the medical decision model, sensitivity and specificity were not significant at selected cut-offs for U-sg and U-osm. At the most accurate cut-off values, 1.015 and 1.020 for U-sg and 700 m(osm)/kg and 800 m(osm)/kg for U-osm, only 65% of the athletes were correctly classified using U-sg and 63% using U-osm, P-osm, U-sg, and U-osm appear sensitive to incremental changes in acute hypertonic dehydration, however, the misclassified outcomes for U-sg and U-osm raise concerns. Research focused on elucidating the factors affecting accurate assessment of hydration status appears warranted.