A Urine Color Chart Is An Accurate Tool For Self-identification Of High Urine Concentration In Athletes

Abstract

PURPOSE: Urine color (Uc) charts can be a reliable field tool to assess urine concentration, but no self-reporting athlete data is available. This study compares Uc scores from athletes against research team scores and urine osmolality values. METHODS: Urine samples were collected from college athletes (n=173, 68% male, median age 20). To standardize Uc scoring, a box was constructed with a set distance (14 inch) towards the 30 ml sample and placed behind a 1.2x1.2 inch opening against a white backdrop. Athletes and two research members independently scored Uc using the chart described by Armstrong in 1994. Differences in researcher Uc were discussed until consensus was established. To control for lighting, two 28-Watt white LED lights were placed aside of the box and the Uc chart. Samples were measured for urine osmolality in duplicate via freezing point depression. RESULTS: Median athlete and researcher scores for Uc values were 2 with an interquartile range (IQR) 1-3 and urine concentration of 744 (474-940) mmol·kg−1. A significant lower number of samples with Uc <2 was reported by athletes (n=60) vs. researchers (n=44), P=0.02. Correlations for Uc against urine osmolality were similar for athlete and researcher scores indicated by a similar r:0.56, P<0.001. Based on athlete score receiver operating characteristics (ROC), Uc has a fair diagnostic capability for identifying urine with an osmolality ≥800 mmol·kg−1 based on an area under the curve (AUC) of 0.71. Contingency tables, based on the ROC optimal threshold for Uc ≥2 (with sensitivity 0.89% and specificity 0.53%) showed 68% among athletes vs. 60% among researchers’ correct classification for being euhydrated or underhydrated. Of the athletes 27% misclassified themselves as being underhydrated (Uc ≥2) with urine concentration below 800 mmol·kg−1, but only 5% of samples were misclassified suggesting proper hydration while osmolality values indicated underhydration. CONCLUSIONS: Validity of reporting Uc by athletes was similar to researchers. Although accuracy could be justified as fair, the Uc misclassification for athletes with high urine osmolality values was minimal. Indicating that Uc can help athletes to self-identify urine concentrations above ≥800 mmol·kg−1 that may predict underhydration. Funded by a Global Sport Institute award at ASU.