Validity of Urinary Biomarkers of Exposure to Tobacco Smoke following Prolonged Storage

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Abstract
Background. The utility of using biomarkers of smoking in epidemiological studies depends not only on the validity and precision of the laboratory procedure but often on the long-term stability of the analytes of interest in stored biological samples. Methods. We retrieved urine samples collected in 1976–1977 from women included in a cohort study in Utrecht and for whom information on smoking status was available. Creatinine and thlocyanate were measured in 1976–1977 on fresh samples. Cotinine and creatinine were analysed in 1988 on urine stored at -20°C. Results. Measurements of creatinine more than 10 years apart showed a correlation of 0.95 and equal means. Cotinine measurements made in 1988 allowed a clear separation of smokers and non-smokers (sensitivity 92%, specificity 100%), suggesting that concentrations retained their discriminant value even after 10 years of storage. Conclusion. These results emphasize the possibilities offered by long-term storage, under proper conditions, of biological samples for subsequent determination of analytes which may emerge as the study progresses.

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