Background: The fraction of exhaled NO (FeNO) is valuable for the follow-up of asthmatic patients. However, its usefulness as a screening tool for asthma is not established.
Methods: We screened a population of 961 university students with a modified European Community Respiratory Health Survey questionnaire that has been previously used for the screening of respiratory symptoms related to asthma. All subjects with a positive answer to at least one question (n = 149) were submitted to FeNO measurement with a portable nitric oxide analyzer. Subsequently, they were submitted to spirometry and evaluated by a physician blinded to FeNO measurements. Seventy students with no respiratory symptoms served as control subjects.
Results: Asthma was diagnosed in 63 subjects, and allergic rhinitis was diagnosed in 57 subjects. Asthmatics presented higher FeNO values than control subjects (median, 20 parts per billion [ppb]; interquartile range, 14 to 31 ppb; vs median, 11 ppb; interquartile range, 7 to 13 ppb, respectively; p < 0.0001), whereas they did not differ from patients with allergic rhinitis (median, 17 ppb; interquartile range, 12 to 23 ppb; p = 0.28). FeNO values > 19 ppb presented 85.2% specificity and 52.4% sensitivity for the diagnosis of asthma (area under the curve [AUC], 0.723). The diagnostic performance of FeNO was better in nonsmokers (AUC, 0.805), yet FeNO values > 25 ppb were characterized by specificity > 90% for the diagnosis of asthma both in smokers and in nonsmokers. However, FeNO was not a good marker for the differentiation between asthma and allergic rhinitis.
Conclusions: FeNO measurement with a portable analyzer is useful for the screening for asthma in young adults. Significant confounding factors are allergic rhinitis and current smoking.