Background: 8-Hydroxydeoxyguanosine (8-OHdG) is a commonly used marker of DNA oxidative stress in epidemiological studies. The aim of this study was to establish whether the urinary concentration of 8-OHdG varies during the first part of the day, when clinical tests are usually performed, and whether it can therefore be measured without bias in spot urine samples.
Material and methods: Spot urine samples were collected using a convenience sample. A linear mixed-effects model for repeated measurements was used to analyze 8-OHdG levels.
Results: A significant increasing trend in time in the 8-OHdG concentration was found among smokers, but not in the case of nonsmokers.
Conclusions: In epidemiological studies on oxidative stress, all participants should collect their early morning urine specimens - before their first cigarette if they are smokers - to gather information on individual background oxidation levels.