Abstract
When selecting the least biased exposure surrogate, for example, the concentration of a biomarker in a urine sample, information on variability must be taken into consideration. We used mixed-effects models to estimate the variability and determinants of urinary cadmium (U-Cd) excretion using spot urine samples collected at six fixed times during 2 days about 1 week apart, from 24 healthy non-smokers. The urine samples were analysed for U-Cd, the concentrations were adjusted for dilution, and the excretion rates were calculated. Between-individual variability dominated the total variability for most measures of U-Cd excretion, especially for 24h urine and first morning samples. The U-Cd excretion showed a circadian rhythm during the day, and time point of sampling was a significant factor in the mixed-effects models, thus a standardised sampling time, such as first morning urine samples, needs to be applied. Gender, urinary flow rate, age, and urinary protein excretions were also significant determinants for U-Cd excretion. The choice of biomarker for U-Cd excretion was found to be more important in individually-based studies of exposure-response relationships than in studies of comparing Cd levels of groups. When planning a study, this variability of U-Cd in spot samples must be acknowledged.
Original language | English |
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Pages (from-to) | 171-179 |
Journal | Journal of Exposure Science & Environmental Epidemiology |
Volume | 24 |
Issue number | 2 |
DOIs | |
Publication status | Published - 2014 |
Subject classification (UKÄ)
- Environmental Health and Occupational Health
Free keywords
- variability
- spot urine
- urinary excretion
- cadmium
- 24h urine
- study
- design