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.