title: Validity of urinary biomarkers of exposure to tobacco smoke following prolonged storage.
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 thiocyanate were measured in 1976-1977 on fresh samples. Cotinine and creatinine were analysed in 1988 on urine stored at -20 degrees 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: International Agency for Research on Cancer, Lyon, France.
authors.forename: E
authors.initials: E
authors.lastname: Riboli
authors.forename: N J
authors.initials: NJ
authors.lastname: Haley
authors.forename: F
authors.initials: F
authors.lastname: De Waard
authors.forename: R
authors.initials: R
authors.lastname: Saracci
mesh_terms: D015415:Biomarkers / Q000652:urine; D003404:Creatinine / Q000652:urine; D015925:Cryopreservation; D005260:Female; D006801:Humans; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012907:Smoking / Q000453:epidemiology / Q000652:urine*; D013861:Thiocyanates / Q000652:urine; D013997:Time Factors
chemical_list: D015415:Biomarkers; D013861:Thiocyanates; D003404:Creatinine; C031760:thiocyanate