Hydration testing in collegiate wrestlers undergoing hypertonic dehydration

Because dehydration (DEH) violates assumptions used in the assessment of body composition, hydration testing has become an integral part of minimal weight (MW) assessment. To determine the accuracy of hydration tests for the detection and quantification of hypertonic DEH. Twenty-five male collegiate wrestlers (mean +/- SD, age: 20.0 +/- 1.4 yr, height: 175.0 +/- 7.1 cm, body mass: 81.7 +/- 15.3 kg) had their hydration assessed under well-controlled conditions of euhydration (EUH) and DEH. The DEH phase occurred on the same day as EUH, after subjects acutely dehydrated 2-6% of body weight through fluid/food restriction and exercise in a hot environment. All hydration tests except plasma potassium significantly increased from EUH to DEH, and meaningful cutoff values could be established for most tests. Cutoff values for urine tests were 586 mOsm.L(-1) for osmolality and 71 mEq.L(-1) for potassium. Plasma cutoff values were 293 mOsm.L(-1) for osmolality, 140 mEq.L(-1) for sodium, 103 mEq.L(-1) for chloride, and 3.5 pg.mL(-1) for arginine vasopressin. For ratio tests, a urine:plasma osmolality of 2.06 and an extracellular:intracellular water of 0.533 measured by the bioelectrical impedance spectroscopy were cutoff values. For urine specific gravity, a cutoff value of 1.020 g.mL(-1) had a sensitivity and specificity of 96% each for the automated harmonic oscillation technique and 87% and 91% (respectively) for the dipstick technique. Protein (by dipstick) was detected in 5% of subjects in EUH, and 100% of subjects in DEH. Correlations between hydration tests and dehydration were only low to moderate. This study supports a specific gravity cutoff of 1.020 g.mL(-1) for the identification of hypertonic DEH. Future research should test the cutoff values established in this study and explore the relationship between DEH and urine protein.