title: Exhaled nitric oxide levels in asthma: Personal best versus reference values.
abstract: BACKGROUND
  Factors affecting the fraction of nitric oxide in exhaled air (FE(NO)) are multiple. Interpreting values when assessing airways disease may be problematic. Clinically optimum levels have not been defined.
  
  
  OBJECTIVE
  We aimed to establish the relationship between predicted values for FE(NO) obtained from equations by Olin et al, Travers et al, and Dressel et al, and normalized levels after oral prednisone. We also compared postprednisone FE(NO) levels with those obtained during optimized treatment with inhaled fluticasone.
  
  
  METHODS
  Data were obtained before and after a trial of oral prednisone (30mg/d for 14 days), and also from a previously published study in which patients had their dose of inhaled corticosteroid adjusted using either FE(NO) or symptoms/lung function to optimize treatment.
  
  
  RESULTS
  Seventy-three patients completed the study. The geometric mean FE(NO) after prednisone (17.7 parts per billion [ppb]; 95% CI, 15.5-20.2) was significantly lower than mean FE(NO) at the optimized fluticasone dose (20.2 ppb; 95% CI, 17.1-23.8; P=.04) and at loss of control (27.6 ppb; 95% CI, 22.8-33.4; P < .001). FE(NO) levels after prednisone did not differ significantly from the predicted values of Olin et al (16.8 ppb, 95% CI, 16.0-17.5; P=.44), but were significantly lower than values of Travers et al (predicted, 21.5 ppb; 95% CI, 20.9-22.2; P=.005) and Dressel et al (predicted, 27.8 ppb; 95% CI, 26.7-28.9; P < .001).
  
  
  CONCLUSIONS
  Optimum FE(NO) levels are best established by using oral rather than inhaled steroid treatment, and these approximate to predicted values from the reference equation by Olin et al. However, at optimized doses of inhaled corticosteroid, although FE(NO) levels were higher than predicted, asthma was well controlled. Targeting FE(NO) on reference values is not justified.
authors.affiliation: Dunedin School of Medicine, University of Otago, Dunedin, New Zealand.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Smith
authors.forename: Jan O
authors.initials: JO
authors.lastname: Cowan
authors.forename: D Robin
authors.initials: DR
authors.lastname: Taylor
mesh_terms: D000280:Administration, Inhalation; D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000368:Aged; D000730:Androstadienes / Q000008:administration & dosage / Q000627:therapeutic use*; D001249:Asthma / Q000175:diagnosis / Q000188:drug therapy* / Q000276:immunology; D001944:Breath Tests; D045853:Exhalation / Q000187:drug effects / Q000502:physiology; D005260:Female; D000068298:Fluticasone; D006801:Humans; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000032:analysis*; D011241:Prednisone / Q000008:administration & dosage / Q000627:therapeutic use*; D012016:Reference Values; D055815:Young Adult
chemical_list: D000730:Androstadienes; D009569:Nitric Oxide; D000068298:Fluticasone; D011241:Prednisone