Exhaled nitric oxide predicts asthma relapse in children with clinical asthma remission

Background: Nitric oxide in exhaled air (FENO) is a marker of eosinophilic airway inflammation. A study was undertaken to determine whether FENO predicts asthma relapse in asymptomatic asthmatic children in whom inhaled corticosteroids are discontinued. Methods: Forty children ( 21 boys) of mean age 12.2 years on a median dose of 400 mg budesonide or equivalent ( range 100 - 400) were included. FENO was measured before and 2, 4, 12, and 24 weeks after withdrawal of steroids. A relapse was defined as more than one exacerbation per month, or need for beta agonist treatment on 4 days per week for at least 2 weeks, or diurnal peak flow variability of >20%. FENO measurements were performed online with an expiratory flow of 50 ml/s. Results: Nine patients relapsed. Two and 4 weeks after withdrawal of steroids geometric mean FENO in children who were about to relapse was higher than in those who did not relapse: 35.3 ppb v 15.7 ppb at 2 weeks ( ratio 2.3; 95% CI 1.2 to 4.1; p = 0.01) and 40.8 ppb v 15.9 ppb at 4 weeks ( ratio 2.6; 95% CI 1.3 to 5.1). An FENO value of 49 ppb at 4 weeks after discontinuation of steroids had the best combination of sensitivity ( 71%) and specificity ( 93%) for asthma relapse. Conclusion: FENO 2 and 4 weeks after discontinuation of steroids in asymptomatic asthmatic children may be an objective predictor of asthma relapse.