title: Are exhaled nitric oxide measurements using the portable NIOX MINO repeatable?
abstract: BACKGROUND
  Exhaled nitric oxide is a non-invasive marker of airway inflammation and a portable analyser, the NIOX MINO (Aerocrine AB, Solna, Sweden), is now available. This study aimed to assess the reproducibility of the NIOX MINO measurements across age, sex and lung function for both absolute and categorical exhaled nitric oxide values in two distinct groups of children and teenagers.
  
  
  METHODS
  Paired exhaled nitric oxide readings were obtained from 494 teenagers, aged 16-18 years, enrolled in an unselected birth cohort and 65 young people, aged 6-17 years, with asthma enrolled in an interventional asthma management study.
  
  
  RESULTS
  The birth cohort participants showed a high degree of variability between first and second exhaled nitric oxide readings (mean intra-participant difference 1.37 ppb, 95% limits of agreement -7.61 to 10.34 ppb), although there was very close agreement when values were categorised as low, normal, intermediate or high (kappa = 0.907, p < 0.001). Similar findings were seen in subgroup analyses by sex, lung function and asthma status. Similar findings were seen in the interventional study participants.
  
  
  CONCLUSIONS
  The reproducibility of exhaled nitric oxide is poor for absolute values but acceptable when values are categorised as low, normal, intermediate or high in children and teenagers. One measurement is therefore sufficient when using categorical exhaled nitric oxide values to direct asthma management but a mean of at least two measurements is required for absolute values.
authors.affiliation: School of Medicine, University of Southampton, Southampton, UK. acs404@soton.ac.uk
authors.forename: Anna
authors.initials: A
authors.lastname: Selby
authors.forename: Bernie
authors.initials: B
authors.lastname: Clayton
authors.forename: Jane
authors.initials: J
authors.lastname: Grundy
authors.forename: Katy
authors.initials: K
authors.lastname: Pike
authors.forename: Kirsty
authors.initials: K
authors.lastname: Drew
authors.forename: Abid
authors.initials: A
authors.lastname: Raza
authors.forename: Ramesh
authors.initials: R
authors.lastname: Kurukulaaratchy
authors.forename: S Hasan
authors.initials: SH
authors.lastname: Arshad
authors.forename: Graham
authors.initials: G
authors.lastname: Roberts
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000175:diagnosis / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D001944:Breath Tests / Q000295:instrumentation*; D002648:Child; D002986:Clinical Trials as Topic; D015331:Cohort Studies; D004867:Equipment Design; D045853:Exhalation; D005260:Female; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000032:analysis*; D015588:Observer Variation; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012129:Respiratory Function Tests; D006113:United Kingdom
chemical_list: D009569:Nitric Oxide