title: Variability of urinary cadmium excretion in spot urine samples, first morning voids, and 24 h urine in a healthy non-smoking population: implications for study design.
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 24 h 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.
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital and Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Akerstrom
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital and Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Barregard
authors.affiliation: Department of Occupational and Environmental Medicine, Lund University Hospital, Lund, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lundh
authors.affiliation: Department of Occupational and Environmental Medicine, Sahlgrenska University Hospital and Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Gerd
authors.initials: G
authors.lastname: Sallsten
mesh_terms: D002104:Cadmium / Q000652:urine*; D002940:Circadian Rhythm; D064368:Healthy Volunteers; D006801:Humans; D012907:Smoking / Q000652:urine
chemical_list: D002104:Cadmium
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