Exhaled nitric oxide and blood eosinophilia: biomarkers of different adult asthma phenotypes

Rationale: Fraction of exhaled nitric oxide (FeNO) and blood eosinophils are increasingly used for phenotyping patients with asthma. In some patients these biomarkers fluctuate over time, whereas in others they are persistently elevated. Whether these biomarker patterns are associated with different asthma phenotypes is unknown. Aim: to compare subjects with persistently high FeNO or blood eosinophils versus fluctuating FeNO or blood eosinophil levels. Methods: 141 adults with mild-moderate asthma were prospectively followed for 5 years. Clinical, functional and inflammatory characteristics were assessed at least twice and compared between patients with persistently high FENO (cut-off 25 ppb) and fluctuating FeNO levels, and between patients with high blood eosinophils (cut-off 0.4x10 9 ) and fluctuating eosinophilia. Chi 2 , student t-test and Mann-Whitney U test were used, as appropriate. Results: 24% and 6% of subjects had persistently high FeNO and eosinophils, respectively. Compared to patients with fluctuating FeNO levels those with persistently high levels were characterized by low BMI (26.5 vs 29.2 p=0.01), less pack years smoked (2 vs 6 p=0.02) and accelerated FEV 1 decline over 5 years (-271ml vs -40ml p=0.03). Patients with persistently high blood eosinophilia were characterized by increased air trapping (FRC %pred 122% vs 83% p=0.04) after 5 years. Conclusion: Asthma patients with persistently high FeNO differ from those with high blood eosinophils, and from those with fluctuating biomarker levels. This suggests that repeated measurements of both FeNO and blood eosinophilis are required to determine the asthma phenotype in adults.