Simultaneously increased fraction of exhaled nitric oxide levels and blood eosinophil counts relate to increased asthma morbidity

Abstract

We have previously described that fraction of exhaled nitric oxide (Feno) levels and blood eosinophil counts offer additive information in relation to asthma and asthma exacerbations when analyzing data from a large population study. We sought to investigate increased Feno levels and blood eosinophil counts in relation to lung function, bronchial hyperresponsiveness (BHR), and asthma control in a cohort of young asthmatic patients. Measurements of Feno levels and blood eosinophil counts were available in 406 subjects (208 women) aged 10 to 35years. Asthma control was assessed through the Asthma Control Test. Moderate-to-severe BHR was defined as a cumulative dose of methacholine of less than 0.3 mg causing an FEV1 decrease of 20%. Subjects with simultaneously increased Feno levels (≥20-25ppb) and blood eosinophil counts (≥0.3×109/L) had a higher prevalence of uncontrolled asthma (Asthma Control Test score, <20) than subjects with singly increased blood eosinophil counts (40.5% vs 21.1%, P=.01). This difference remained significant (P=.006), and a significant difference was also found between subjects with both increased Feno levels and blood eosinophil counts and subjects with normal Feno levels and blood eosinophil counts (P=.02) after adjusting for confounders. Having increased Feno levels and blood eosinophil counts related to a higher prevalence of moderate-to-severe BHR than having normal Feno levels and blood eosinophil counts or singly increased Feno levels or blood eosinophil counts (85.7% vs 35.8% or 63.3% or 60%, P<.05 all comparisons). We have shown that simultaneously increased local (Feno) and systemic (blood eosinophil) markers of type 2 inflammation related to a higher likelihood of BHR and uncontrolled asthma in a large cohort of young asthmatic patients.