Urinary Indices of Hydration Status

TLDR

A simple, universally accepted method to assess human hydration status would benefit athletes and researchers. The authors conducted two laboratory studies and one field study to evaluate urine color as a hydration indicator and to assess interchangeability among urine color, osmolality, and specific gravity. Urine color, osmolality, and specific gravity did not correlate with plasma osmolality, sodium, or hematocrit, yet urine color correlated strongly with osmolality and specific gravity, indicating it can be used in field settings while osmolality and specific gravity are interchangeable for hydration assessment.

Abstract

Athletes and researchers could benefit from a simple and universally accepted technique to determine whether humans are well-hydrated, euhydrated, or hypohydrated. Two laboratory studies (A, B) and one field study (C) were conducted to determine if urine color (Ucol) indicates hydration status accurately and to clarify the interchangeability of Ucol, urine osmolality (Uosm), and urine specific gravity (Usg) in research. Ucol, Uosm, and Usg were not significantly correlated with plasma osmolality, plasma sodium, or hematocrit. This suggested that these hematologic measurements are not as sensitive to mild hypohydration (between days) as the selected urinary indices are. When the data from A, B, and C were combined, Ucol was strongly correlated with Usg and Uosm. It was concluded that (a) Ucol may be used in athletic/industrial settings or field studies, where close estimates of Usg or Uosm are acceptable, but should not be utilized in laboratories where greater precision and accuracy are required, and (b) Uosm and Usg may be used interchangeably to determine hydration status.