The value of exhaled nitric oxide to identify asthma in smoking patients with asthma-like symptoms

Respir Med. 2012 Jun;106(6):794-801. doi: 10.1016/j.rmed.2012.02.009. Epub 2012 Mar 8.


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.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Asthma / diagnosis*
  • Asthma / physiopathology
  • Biomarkers / metabolism
  • Breath Tests* / methods
  • Bronchial Hyperreactivity / metabolism
  • Diagnosis, Differential
  • Eosinophils / pathology
  • Female
  • Forced Expiratory Volume / physiology
  • Humans
  • Hypersensitivity, Immediate / metabolism
  • Leukocyte Count
  • Male
  • Nitric Oxide / metabolism*
  • Smoking / adverse effects
  • Smoking / metabolism*
  • Smoking / physiopathology
  • Smoking Cessation
  • Vital Capacity / physiology
  • Young Adult


  • Biomarkers
  • Nitric Oxide