Criterion values for urine-specific gravity and urine color representing adequate water intake in healthy adults

Growing evidence suggests a distinction between water intake necessary for maintaining a euhydrated state, and water intake considered to be adequate from a perspective of long-term health. Previously, we have proposed that maintaining a 24-h urine osmolality (U(Osm)) of ⩽500 mOsm/kg is a desirable target for urine concentration to ensure sufficient urinary output to reduce renal health risk and circulating vasopressin. In clinical practice and field monitoring, the measurement of U(Osm) is not practical. In this analysis, we calculate criterion values for urine-specific gravity (U(SG)) and urine color (U(Col)), two measures which have broad applicability in clinical and field settings. A receiver operating characteristic curve analysis performed on 817 urine samples demonstrates that a U(SG) ⩾1.013 detects U(Osm)>500 mOsm/kg with very high accuracy (AUC 0.984), whereas a subject-assessed U(Col)⩾4 offers high sensitivity and moderate specificity (AUC 0.831) for detecting U(Osm) >500 m Osm/kg.