Method: Data from non-smoking patients with asthmatic symptoms from 2011 to 2014 at a single tertiary center was analyzed. FeNO levels were classified into 3 groups (high; FeNO≥50ppb, intermediate; 25ppb≤FeNO<50ppb, and low; FeNO<25ppb). The cutoff value differentiating high and low ISE was 3% of eosinophils in induced sputum. Combining the two criteria, patients were classified into 3 groups; concordant (high FeNO and high ISE, or low FeNO and low ISE), intermediate (intermediate FeNO and either level of ISE), and discordant (high FeNO and low ISE, or low FeNO and high ISE).
Result: Among the total of 591 patients, 76 (12.8%) patients were classified into discordant group. Among them, 67 (88.2%) showed high FeNO and low ISE, while only 9 (11.8%) showed low FeNO and high ISE. Comparison between concordant and discordant groups showed that male sex, absence of airway hyperresponsiveness, increased age, and increased neutrophil count in sputum were more frequently seen in discordant group. Current or previous use of corticosteroid, presence of atopy, and salivary contamination of induced sputum were not significantly different between the two groups.
Conclusion: Discordance between FeNO and ISE was observed in quite a few patients. Most of the discordance results from high FeNO and low ISE. Further study is necessary to find a proper method to assess airway inflammation in this subset of patients.