Fractional exhaled nitric oxide and blood eosinophils in relation to lung function, allergy and nasal polyps in asthma

Background: Type 2 inflammation plays a central role in asthma, but blood eosinophil count (BEC) and fractional exhaled nitric oxide (Feno) levels may reflect different type 2 pathways. Their associations with different asthma characteristics in unselected populations remain unclear. Objectives: To examine how BEC and Feno, independently and synergistically, are related to lung function, allergy, and nasal polyps in a population-based asthma cohort. Methods: Data were analyzed from 1567 participants with physician-diagnosed asthma in the West Sweden Asthma Study. Lung function, bronchodilator responsiveness, and presence of allergy and nasal polyps were evaluated across categories of BEC and Feno labeled as low, medium, or high using various cutoffs. Associations were assessed using linear and logistic regression models in participants who were inhaled corticosteroid (ICS)-naive and ICS-treated separately. Results: and forced vital capacity percentages and a higher prevalence of clinical allergy, with consistent effects across a range of cutoff values. Conclusion: BEC and Feno reflect distinct yet complementary aspects of type 2 inflammation in asthma. These findings support the joint use of BEC and Feno for obstructive airway diseases phenotyping.