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.
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.
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.
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.