title: Interlaboratory comparability of serum cotinine measurements at smoker and nonsmoker concentration levels: a round-robin study.
abstract: BACKGROUND
  Cotinine, the primary proximate metabolite of nicotine, is commonly measured as an index of exposure to tobacco in both active users of tobacco and nonsmokers with possible exposure to secondhand smoke (SHS). A number of laboratories have implemented analyses for measuring serum cotinine in recent years, but there have been few interlaboratory comparisons of the results. Among nonsmokers exposed to SHS, the concentration of cotinine in blood can be quite low, and extensive variability in these measurements has been reported in the past.
  
  
  METHODS
  In this study, a group of seven laboratories, all experienced in serum cotinine analysis, measured eight coded serum pools with concentrations ranging from background levels of about 0.05 ng/ml to relatively high concentrations in the active smokers range. All laboratories used either gas-liquid chromatography with nitrogen-phosphorus detection or liquid chromatography with mass spectrometric detection.
  
  
  RESULTS
  All seven laboratories reliably measured the cotinine concentrations in samples that were within the range of their methods. In each case, the results for the pools were correctly ranked in order, and no significant interlaboratory bias was observed at the 5% level of significance for results from any of the pools.
  
  
  CONCLUSIONS
  We conclude that present methods of chromatographic analysis of serum cotinine, as used by these experienced laboratories, are capable of providing accurate and precise results in both the smoker and the nonsmoker concentration range.
authors.affiliation: Division of Laboratory Science , National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA. jtb2@cdc.gov
authors.forename: John T
authors.initials: JT
authors.lastname: Bernert
authors.forename: Peyton
authors.initials: P
authors.lastname: Jacob
authors.forename: David B
authors.initials: DB
authors.lastname: Holiday
authors.forename: Neal L
authors.initials: NL
authors.lastname: Benowitz
authors.forename: Connie S
authors.initials: CS
authors.lastname: Sosnoff
authors.forename: Mira V
authors.initials: MV
authors.lastname: Doig
authors.forename: Colin
authors.initials: C
authors.lastname: Feyerabend
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Aldous
authors.forename: Mehran
authors.initials: M
authors.lastname: Sharifi
authors.forename: Mark D
authors.initials: MD
authors.lastname: Kellogg
authors.forename: Loralie J
authors.initials: LJ
authors.lastname: Langman
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003367:Cotinine / Q000097:blood*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D007753:Laboratories / Q000458:organization & administration* / Q000592:standards; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods* / Q000592:standards; D014028:Tobacco Smoke Pollution / Q000032:analysis; D014481:United States
chemical_list: D014028:Tobacco Smoke Pollution; D003367:Cotinine