Exhaled Nitric Oxide Utility in Predicting Asthma Exacerbations

Exhaled nitric oxide (eNO) has been shown to be a marker of eosinophilic inflammation in asthma. Prior studies have yielded mixed results regarding whether eNO levels are predictive of future asthma exacerbations. We hypothesized that there is an association between eNO level and asthma exacerbations, and that this association varies by FEV1. We conducted a retrospective chart review of 161 patients from a large allergy and asthma practice in Seattle. Patients were 18 years and older, had a diagnosis of asthma, and had undergone eNO testing between January 2012 and June 2014. Patients were stratified by FEV1 level: < 60%, between 60-80%, and >80%. eNO was modeled continuously rather than by choosing pre-determined cutoff values, as there is not an established clinically relevant threshold for eNO. Poisson regression models with robust standard errors were used to study the adjusted association between the number of exacerbations requiring prednisone and eNO. We controlled for FEV1, gender, height, BMI, smoking history, history of IgE-mediated allergies, allergic rhinitis, and positive inhalant skin tests. There was no association between eNO levels and number of asthma exacerbations (p = 0.98). There was also insufficient evidence to conclude that the associations between number of exacerbations and eNO among individuals with FEV1 60-80% or FEV1 <60% differed from patients with FEV1 >80% (p=0.06). We did not find eNO levels to be a useful clinical marker in predicting risk of future asthma exacerbations, regardless of FEV1 level.