Classification and Temporal Variability in Urinary 8-oxodG and 8-oxoGuo: Analysis by UHPLC-MS/MS.

Oxidative stress damage has been found to be associated with exposure of children to environmental pollutants, but there are few data on the variability of urinary oxidative stress biomarkers and the accuracy of biomarker concentration classification. We performed a longitudinal study in Chinese school-aged children to investigate the variability of urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydroguanosine (8-oxoGuo) concentrations and the ability of a single first morning urine sample to assess accuracy and sensitivity of biomarkers concentration classification. After adjusting for both creatinine and specific gravity, we characterized the distribution and reproducibility of repeated measurement of 8-oxodG and 8-oxoGuo by using intraclass correlation coefficients (ICCs) derived from linear mixed model and performed surrogate category analyses to determine whether a single spot sample could accurately classify 8-oxodG and 8-oxoGuo levels. Results indicated that the geometric mean (GM) concentrations of 8-oxodG and 8-oxoGuo were 3.865 ng/mL and 5.725 ng/mL, respectively. High variability of 8-oxodG and 8-oxoGuo was observed in the single spot first morning urine sample (ICC = 0.25 and 0.18, respectively). Three repeated urinary specimens achieved sensitivity of 0.87 for 8-oxodG and 0.83 for 8-oxoGuo in low tertile and sensitivity of 0.78 in high tertile. But classification in medium tertile was less accurate for both 8-oxodG and 8-oxoGuo. In conclusion, high variability of urinary 8-oxodG and 8-oxoGuo levels results in repeated samplings needed for accurate classification.