Fractional Exhaled Nitric Oxide in Children with Non-Cystic Fibrosis Bronchiectasis: Associations with Etiology, Lung Function, and CT Extent

Background/Objectives: Childhood non-cystic fibrosis (non-CF) bronchiectasis is clinically heterogeneous. We aimed to describe fractional exhaled nitric oxide (FeNO) levels in affected children and examine associations with etiology, spirometry, and CT-defined disease extent. Methods: This single-center prospective observational study included 100 clinically stable children aged 6–18 years with CT-confirmed non-CF bronchiectasis evaluated between September 2014 and December 2015. FeNO was measured before spirometry using an online single-breath electrochemical technique. Chest CT was reviewed at the lobar level, with the lingula counted separately, and disease extent was summarized by the number of involved lobar regions. Associations were assessed using Spearman correlation and non-parametric tests. Results: Mean age was 14.9 ± 2.0 years, 55% were male, and mean FeNO was 20.9 ± 14.0 ppb. FeNO correlated positively with FEV1 (% predicted), FVC (% predicted), and FEF25–75 (% predicted) (all p < 0.01). FeNO was higher in males and adolescents than in females and younger children, respectively. FeNO did not differ by CT-defined lobar extent. It was lower in primary ciliary dyskinesia than in asthma overlap. Overall, 82% of the cohort received an ICS-containing maintenance regimen and household tobacco smoke exposure was present in 58%. Conclusions: FeNO was associated with selected functional indices and etiologic subgroups, but not with CT-defined structural extent, suggesting a greater role in clinical phenotyping than in reflecting radiologic burden. Rather than reflecting overall disease severity, FeNO may be more relevant as a marker of T2-leaning airway inflammatory phenotype in selected children with non-CF bronchiectasis. These findings should be interpreted as exploratory and hypothesis-generating, particularly for etiologic subgroup comparisons and for FeNO interpretation in the setting of treatment and environmental confounding.