Dehydration is how you define it: comparison of 318 blood and urine athlete spot checks.

Unlabelled: Clinical medicine defines dehydration using blood markers that confirm hypertonicity (serum sodium concentration ([Na])>145 mmol/L) and intracellular dehydration. Sports medicine equates dehydration with a concentrated urine as defined by any urine osmolality (UOsm) ≥700 mOsmol/kgHO or urine specific gravity (USG) ≥1.020.