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 ( F eNO ) 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 F eNO <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 F eNO ≥25 ppb or blood eosinophils ≥0.3×109  cells·L-1 and 2.14 (1.47-3.10) for individuals with F eNO ≥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 F eNO 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.