Seasonality and environmental determinants of exhaled nitric oxide in individuals with and without chronic respiratory diseases

Background and Objective: Fractional exhaled nitric oxide (FeNO) is a biomarker of type-2 lung inflammation. Standardized measurement is essential for accurate diagnosis and monitoring. We assess seasonality and environmental determinants of FeNO in individuals with and without chronic respiratory diseases in the general population. Methods: This is a cross-sectional study on 412 individuals with chronic respiratory diseases (asthma, chronic bronchitis/chronic obstructive pulmonary disease, rhinitis) and 605 individuals without these conditions. Participants, aged 20–65 years, were recruited in the Gene-Environment Interactions in Respiratory Diseases study in Verona, Italy (2008–2014). Geocoded residential addresses were linked to daily PM 10 and air temperature at the time of the clinical examination using previously developed spatiotemporal models. Associations with log-FeNO were analyzed using adjusted linear regression, accounting for seasonality and disease status. Results: FeNO levels were higher in subjects with respiratory diseases during the warm season, even after adjusting for pollen exposures; a milder seasonal pattern was observed in subjects without chronic respiratory diseases ( P for interaction = 0.001). A 10 μg/m 3 increase in mean PM 10 concentration at lag 0–1 (day of FeNO measurement and day before) was associated with a 3% higher FeNO concentration (Ratio of Geometric Means, RGM: 1.03, 95% confidence interval: 1.00, 1.06) after adjusting for seasonality. Conclusion: FeNO is a sensitive biomarker of environmental exposures. Overlooking seasonality and environmental factors might impact clinical decision-making in chronic respiratory diseases.