Combined value of exhaled nitric oxide and blood eosinophils in chronic airway disease: the Copenhagen General Population Study

We investigated whether the combination of increased exhaled nitric oxide fraction (FeNO) level and blood eosinophil count had an additive value in chronic airway disease in the general population.We included 4677 individuals aged 20-100 years from the Copenhagen General Population Study. Based on pre- and post-bronchodilator spirometry, self-reported asthma and smoking history, participants were subdivided into healthy never-smokers (n=1649), healthy ever-smokers (n=1581), asthma (n=449), chronic obstructive pulmonary disease (COPD) (n=404), asthma-COPD overlap (ACO) (n=138) and nonspecific airflow limitation (n=456).Compared to individuals with FeNO <25 ppb and blood eosinophils <0.3×109 cells·L-1, age- and sex-adjusted odds ratios (95% CI) for wheezing were 1.54 (1.29-1.84) for individuals with FeNO ≥25 ppb or blood eosinophils ≥0.3×109 cells·L-1 and 2.14 (1.47-3.10) for individuals with FeNO ≥25 ppb and blood eosinophils ≥0.3×109 cells·L-1 Corresponding odds ratios were 1.13 (0.91-1.41) and 1.83 (1.20-2.79) for sputum production, 1.54 (1.22-1.94) and 3.26 (2.16-4.94) for asthma, 1.03 (0.80-1.32) and 0.67 (0.36-1.27) for COPD and 1.32 (0.88-1.96) and 2.14 (1.05-4.36) for ACO. Among individuals reporting respiratory symptoms, predicting the type of chronic airway disease did not differ between the two biomarkers and did not improve by combining them.Combination of FeNO and blood eosinophils may have an additive value in characterising chronic airway disease in the general population but still needs to be investigated further with regard to clinical application.