Background: The appropriate reference value of the urinary protein-to-creatinine ratio (PCR) for proteinuria may change when the urinary pyrogallol red (PR) protein assay method is changed to the benzethonium chloride method (BC). This study aimed to evaluate the difference between BC-based PCR (BC-PCR) and PR-based PCR (PR-PCR) values in children.

Methods: We compared the BC-PCR and PR-PCR values in the same first-morning urine samples without significant proteinuria in school urine screening settings. The upper limit of the reference values was set at the 97.5th percentile.

Results: Notably, 133 samples from 124 individuals (female: 62%, age: median 12.3 years, range 6.3-16.9 years) were collected between August 2020 and October 2022. The diagnoses included 34 normal individuals and 99 with asymptomatic hematuria. The urinary protein (UP) concentrations measured using the BC (BC-UP) and PR (PR-UP) methods were in a linear relationship; however, the BC-UP concentrations were higher than the PR-UP concentrations (mean of differences: 11.2, 95% confidence interval (CI): 11.0-13.4 mg/dL). Also, the BC-PCR values were higher than the PR-PCR values (mean of differences: 0.090, 95% CI: 0.082-0.098 g/gCr). The BC-PCR showed a body-size-related decrease, reflecting a body-size-related urinary creatinine increase. The suggested BC-PCR reference values for proteinuria were 0.25 and 0.17 g/gCr for elementary (6-12.4 years) and junior high school students (12.5-16 years), respectively. These values were higher than those of the PR-PCR and need further studies.

Conclusions: When evaluating PCR results, the urinary protein assay should be stated.