VALIDITY OF URINARY BIOMARKERS OF EXPOSURE TO TOBACCO-SMOKE FOLLOWINGPROLONGED STORAGE

Background. The utility of using biomarkers of smoking in epidemiologi cal studies depends not only on the validity and precision of the labo ratory 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 i n Utrecht and for whom information on smoking status was available, Cr eatinine and thiocyanate were measured in 1976-1977 on fresh samples. Cotinine and creatinine were analysed in 1988 on urine stored at -20 d egrees C, Results, Measurements of creatinine more than 10 years apart showed a correlation of 0.95 and equal means, Cotinine measurements m ade in 1988 allowed a clear separation of smokers and non-smokers (sen sitivity 92%, specificity 100%), suggesting that concentrations retain ed their discriminant value even after 10 years of storage. Conclusion . These results emphasize the possibilities offered by long-term stora ge, under proper conditions, of biological samples for subsequent dete rmination of analytes which may emerge as the study progresses.