title: The value of exhaled nitric oxide to identify asthma in smoking patients with asthma-like symptoms.
abstract: BACKGROUND
  The fraction of nitric oxide in exhaled air (FeNO) is used in asthma diagnosis and management. Smoking reduces FeNO and 20-35% of asthmatics are smoking. However no guidelines exist on the diagnostic value of FeNO in smokers. Therefore we assessed the value of FeNO to diagnose asthma in a population of subjects with asthma-like symptoms and different smoking habits.
  
  
  METHODS
  Measurements of FeNO, lung function, bronchial responsiveness and allergy testing were performed in 282 subjects (108 never-, 62 ex- and 112 current smokers) aged 14-44 years, with symptoms suggestive of asthma. These subjects were a subset of subjects reporting respiratory symptoms (n = 686) in a random population sample (n = 10,400).
  
  
  RESULTS
  A diagnosis of asthma was given to 96 of the 282 subjects. Subjects with asthma had higher FeNO levels than subjects with non-specific asthma symptoms in all three smoking strata (p < 0.001), with a percentual increase of FeNO by 76% in never-, 71% in ex- and 60% in current smokers. The area under the ROC-curve was similar in never-, ex- and current smokers (0.72 vs. 0.74 vs. 0.70). The cut-offs were approximately 30% lower for either 90% specificity (22 vs. 31 ppb) or 90% sensitivity (7 vs. 10 ppb) in current vs. never-smokers.
  
  
  CONCLUSIONS
  FeNO could differentiate asthmatic subjects from non-asthmatic subjects with asthma-like symptoms equally well in both never- and current smokers within a random population sample. The FeNO cut-off levels needed in order to achieve high sensitivity or specificity were lower in current smokers.
authors.affiliation: Department of Medical Sciences, Clinical Physiology, Uppsala University, Uppsala, Sweden. Andrei.Malinovschi@medsci.uu.se
authors.forename: Andrei
authors.initials: A
authors.lastname: Malinovschi
authors.forename: Vibeke
authors.initials: V
authors.lastname: Backer
authors.forename: Henrik
authors.initials: H
authors.lastname: Harving
authors.forename: Celeste
authors.initials: C
authors.lastname: Porsbjerg
mesh_terms: D000293:Adolescent; D000328:Adult; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology; D015415:Biomarkers / Q000378:metabolism; D001944:Breath Tests / Q000379:methods; D016535:Bronchial Hyperreactivity / Q000378:metabolism; D003937:Diagnosis, Differential; D004804:Eosinophils / Q000473:pathology; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000378:metabolism; D007958:Leukocyte Count; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D012907:Smoking / Q000009:adverse effects / Q000378:metabolism* / Q000503:physiopathology; D016540:Smoking Cessation; D014797:Vital Capacity / Q000502:physiology; D055815:Young Adult
chemical_list: D015415:Biomarkers; D009569:Nitric Oxide