title: Factors affecting exhaled nitric oxide measurements: the effect of sex.
abstract: BACKGROUND
  Exhaled nitric oxide (F(E)NO) measurements are used as a surrogate marker for eosinophilic airway inflammation. However, many constitutional and environmental factors affect F(E)NO, making it difficult to devise reference values. Our aim was to evaluate the relative importance of factors affecting F(E)NO in a well characterised adult population.
  
  
  METHODS
  Data were obtained from 895 members of the Dunedin Multidisciplinary Health and Development Study at age 32. The effects of sex, height, weight, lung function indices, smoking, atopy, asthma and rhinitis on F(E)NO were explored by unadjusted and adjusted linear regression analyses.
  
  
  RESULTS
  The effect of sex on F(E)NO was both statistically and clinically significant, with F(E)NO levels approximately 25% less in females. Overall, current smoking reduced F(E)NO up to 50%, but this effect occurred predominantly in those who smoked on the day of the F(E)NO measurement. Atopy increased F(E)NO by 60%. The sex-related differences in F(E)NO remained significant (p < 0.001) after controlling for all other significant factors affecting F(E)NO.
  
  
  CONCLUSIONS
  Even after adjustment, F(E)NO values are significantly different in males and females. The derivation of reference values and the interpretation of FENO in the clinical setting should be stratified by sex. Other common factors such as current smoking and atopy also require to be taken into account.
authors.affiliation: Department of Respiratory Medicine, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand. robin.taylor@stonebow.otago.ac.nz
authors.forename: D Robin
authors.initials: DR
authors.lastname: Taylor
authors.forename: Piush
authors.initials: P
authors.lastname: Mandhane
authors.forename: Justina M
authors.initials: JM
authors.lastname: Greene
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Hancox
authors.forename: Sue
authors.initials: S
authors.lastname: Filsell
authors.forename: Christene R
authors.initials: CR
authors.lastname: McLachlan
authors.forename: Avis J
authors.initials: AJ
authors.lastname: Williamson
authors.forename: Jan O
authors.initials: JO
authors.lastname: Cowan
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Smith
authors.forename: Malcolm R
authors.initials: MR
authors.lastname: Sears
mesh_terms: D000328:Adult; D001944:Breath Tests / Q000379:methods; D015331:Cohort Studies; D045853:Exhalation / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000032:analysis* / Q000502:physiology*; D012107:Research Design; D012727:Sex Characteristics
chemical_list: D009569:Nitric Oxide