FIGURE 1

Definitions of 24-h hydration status: In a subject individual minimum and maximum 24-h urine osmolality characterise 24-h hydration status of hypohydration, euhydration and hyperhydration. In a group in which only mean and standard deviation values of minimum and maximum urinary osmolality of a representative subgroup of subjects are known, three categories of 24-h hydration can be characterised using data of Uosm: risk of hypohydration (Uosmmean-2 s.d. value of maximum Uosm), euhydration (mean -2 s.d. value of maximum Usom>Uosm>mean +2 s.d. value of minimum Uosm) and risk of hyperhydration (Uosmmean +2 s.d. value of minimum Uosm). Additional clinical or biochemical signs of hypo(hyper)-hydration are necessary to diagnose hypo(hyper)-hydration in a subject of this life stage and gender group.