title: Assessing smoking status in children, adolescents and adults: cotinine cut-points revisited.
abstract: OBJECTIVE
  To reassess saliva cotinine cut-points to discriminate smoking status. Cotinine cut-points that are in use were derived from relatively small samples of smokers and non-smokers 20 or more years ago. It is possible that optimal cut-points may have changed as prevalence and exposure to passive smoking have declined.
  
  
  METHODS
  Cross-sectional survey of the general population, with assessment of self-reported smoking and saliva cotinine.
  
  
  METHODS
  A total of 58 791 respondents aged 4 years and older in the Health Survey for England for the years 1996-2004 who provided valid saliva cotinine specimens.
  
  
  METHODS
  Saliva cotinine concentrations, demographic variables, self-reported smoking, presence or absence of smoking in the home, a composite index of social disadvantage derived from occupation, housing tenure and access to a car.
  
  
  RESULTS
  A cut-point of 12 ng/ml performed best overall, with specificity of 96.9% and sensitivity of 96.7% in discriminating confirmed cigarette smokers from never regular smokers. This cut-point also identified correctly 95.8% of children aged 8-15 years smoking six or more cigarettes a week. There was evidence of substantial misreport in claimed ex-smokers, especially adolescents (specificity 72.3%) and young adults aged 16-24 years (77.5%). Optimal cut-points varied by presence (18 ng/ml) or absence (5 ng/ml) of smoking in the home, and there was a gradient from 8 ng/ml to 18 ng/ml with increasing social disadvantage.
  
  
  CONCLUSIONS
  The extent of non-smokers' exposure to other people's tobacco smoke is the principal factor driving optimal cotinine cut-points. A cut-point of 12 ng/ml can be recommended for general use across the whole age range, although different cut-points may be appropriate for population subgroups and in societies with differing levels of exposure to secondhand smoke.
authors.affiliation: Health Behaviour Research Centre, and Department of Epidemiology and Public Health, University College London, London, UK. martin.jarvis@ucl.ac.uk
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Jarvis
authors.forename: Jennifer
authors.initials: J
authors.lastname: Fidler
authors.forename: Jennifer
authors.initials: J
authors.lastname: Mindell
authors.forename: Colin
authors.initials: C
authors.lastname: Feyerabend
authors.forename: Robert
authors.initials: R
authors.lastname: West
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000032:analysis; D002648:Child; D002675:Child, Preschool; D003367:Cotinine / Q000032:analysis*; D003430:Cross-Sectional Studies; D004781:Environmental Exposure; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012463:Saliva / Q000737:chemistry*; D012907:Smoking / Q000378:metabolism*; D014028:Tobacco Smoke Pollution / Q000706:statistics & numerical data; D006113:United Kingdom; D055815:Young Adult
chemical_list: D015415:Biomarkers; D014028:Tobacco Smoke Pollution; D003367:Cotinine