Elevated fractional exhaled nitric oxide is prevalent in those with mild-to-moderate asthma with self-reported asthma control

<bold>Introduction:</bold> Elevated fractional exhaled nitric oxide (FeNO) identifies an asthma population at risk of exacerbations and lung function loss, independent of daily symptom control. The prevalence of elevated FeNO in nonsevere asthma is not well described. <bold>Aims:</bold> Determine the proportion of participants with mild-to-moderate asthma who self-reported controlled asthma with elevated FeNO. <bold>Methods:</bold> This post hoc analysis considered FeNO assessed in 769 participants with mild-to-moderate asthma (inhaled corticosteroid [ICS] fluticasone furoate ≤500 µg/day or equivalent ICS) self-reported as controlled, recruited at one center by public advertisement for a prescreening assessment of a Phase 1b study (<ext-link>NCT05366764</ext-link>). Background asthma treatment and blood eosinophils (EOS) were collected from those with FeNO ≥25 ppb and available data. <bold>Results:</bold> Median FeNO was 20 (4-301) ppb. Normal FeNO (<25 ppb) was observed in 58% of participants, whereas elevated levels of ≥25, ≥35, and ≥50 ppb were observed in 42%, 29%, and 19%, respectively. Among those with FeNO ≥25 ppb, asthma treatment data were available for 211 participants (66%): 97 (46%) were ICS naïve, 8 (4%) were on ICS PRN, 84 (40%) were on low-dose ICS, and 22 (10%) were on medium-dose ICS. ICS exposure was similar regardless of FeNO cutoffs. EOS data (109 cells/L) was available for 52 participants (16%) with FeNO ≥25 ppb and was 150-300 in 44% and ≥300 in 42% of participants. <bold>Conclusion:</bold> Almost half of participants with mild-to-moderate asthma had elevated FeNO despite reporting controlled asthma. Most with FeNO ≥25 ppb also had EOS ≥150. Future studies are needed to understand the clinical relevance of these findings.