Context: Urine color (Uc) is used to asses urine concentration when lab techniques are not feasible.

Objective: To compare the accuracy of Uc scoring using four different light conditions and two different scoring techniques with a 7-color Uc chart. Additionally to assess the results' generalizability, a subsample was compared to scores obtained from fresh samples.

Design: Descriptive laboratory study.

Samples: 178 previously frozen urine samples were scored and n=78 samples were compared to its own fresh outcomes.

Main outcome measure: Urine color and accuracy for classifying urine samples were calculated using receiver operating characteristics (ROC) analysis, allowing to compare the diagnostic capacity against a 1.020 urine specific gravity (USG) cut-off and defining optimal Uc cut-off value.

Results: Uc was significantly different between light conditions (P<0.01), with the highest accuracy (80.3%) of correctly classifications of low or high urine concentrations occurring at the brightest light condition. Lower light intensity scored 1.5–2 shades darker on a 7-color Uc scale than bright conditions (P<0.001), with urine color but no further practical differences for accuracy between scoring techniques. Frozen was 0.5–1 shade darker than freshly measured Uc (P<0.004), but they were moderately correlated (r=0.64). A Bland-Altman plot showed that reporting bias mainly affects darker Uc without impacting the diagnostic ability of the method.

Conclusions: Uc scoring, accuracy and Uc cut-off values are affected by lighting condition but not by scoring technique, with higher accuracy and a one-shade lower Uc cut-off value at the brightest light (i.e. LED flashlight).

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Competing Interests

Conflict of interest statement

The authors report no conflict of interest in this project.