Subjective vs. Objective Urine Color: Effect of Hydration Status

Purpose: To investigate the validity of urine color as a metric of hydration status using CIE L*a*b* color space, as compared to the commonly used subjective 8-point scale. Methods: A total of 151 urine samples were collected from subjects (N=28) in various states of hydration. Urine osmolality and urine specific gravity (USG) were measured in each sample. Urine color was assessed by the subjective 8-point urine color scale and quantified using CIE L*a*b* color space. RESULTS: The correlation between the CIE b*-value and urine osmolality (rs=0.89) was determined to be significantly (p=0.004) greater than the correlation between the subjective 8-point urine color scale and urine osmolality (rs=0.85). The correlation between the CIE b*-value and USG (rs=0.90) was also determined to be significantly (p < 0.001) greater than the correlation between the urine color chart and USG (rs=0.84). Lastly, the correlation between urine color as determined by the 8-point subjective urine color chart and the CIE b*-value had a strong relationship (rs=0.92). Conclusions: The correlations of the quantitative CIE b*-value with urine osmolality and USG were significantly greater than the correlations with the 8-point subjective urine color scale. This suggests that a quantitative measurement of urine color via spectrophotometry is a better measure for assessing hydration status vs. subjective determination of urine color. The results of the current study raise the possibility of spectrophotometry as an additional non-invasive method of determining hydration status.