Subjective vs. Objective Urine Color: Effect of Hydration Status

Tory Edwards,Rebekah Belasco,Michael Buono,Alfonso Joaquin Munoz,Vernon Rayo

doi:10.11648/j.aap.20200502.12

Abstract

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.

Highlights

Urine color (Ucol) has been previously examined as a potential indicator of hydration status by comparing it to several established laboratory measures including urine specific gravity (USG) and urine osmolality
The 8-point scale [1] and urine osmolality had a strong relationship (Figure 1), but urine osmolality had a stronger correlation with the CIE b*-value (Figure 2)
The results of the current study illustrate that both subjective (i.e., 8-point urine color scale) and quantitative (i.e., CIE L*a*b* color space b*-value) measures are significantly correlated to established measures of hydration, as seen in Figures 1 and 2

Summary

Introduction

Urine color (Ucol) has been previously examined as a potential indicator of hydration status by comparing it to several established laboratory measures including urine specific gravity (USG) and urine osmolality. Studies have shown that Ucol measured by a subjective urine color chart can, in some cases, be a valid indicator of hydration status in specific populations, such as young, male athletes and elderly women [2,3,4,5,6,7,8,9]. The relationship between Ucol and USG were measured from daily urine samples for eight weeks from Caucasian nursing home residents (N=98) [7]. There was a significant correlation between Ucol and USG in all females while only males with adequate renal function had a significant, but weak, correlation (r=0.39). As this study was only conducted in a Caucasian, elderly population, the effects of ethnicity and age on the Ucol chart’s relationship to USG remains unclear. Fortes et al [10] took a convenience urine sample in adults, 60 years and older, (N=130) upon admission to a hospital and participants were

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