Exhaled nitric oxide levels correlate with measures of disease control in asthma

Background: Asthma guidelines emphasize maintaining disease control. However, objective measures of asthma disease control are lacking. Objective: We sought to examine the relationship between exhaled nitric oxide (NO) levels and measures of asthma disease control versus asthma disease severity. Methods: We performed a cross-sectional study of 100 patients (age range, 7-80 years) with asthma. We administered a questionnaire to identify characteristics of asthma, performed spirometric testing before and after administration of a bronchodilator, and measured exhaled NO levels in all participants. Results: Exhaled NO was significantly correlated with the following markers of asthma disease control: asthma symptoms within the past 2 weeks (P = .02), dyspnea score (P = .02), daily use of rescue medications (P = .01), and reversibility of airflow obstruction (P = .02). Exhaled NO levels were not correlated with the following markers of asthma disease severity: history of respiratory failure (P = .20), health care use (P = .08), fixed airflow obstruction (P = .91), or a validated asthma severity score (P = .19). Markers with relevance to both disease control and severity showed either a weak correlation (FEV₁ and FEV₁ percent predicted) or no correlation (controller drug use) with exhaled NO. Conclusion: We conclude that exhaled NO levels are correlated predominantly with markers of asthma control rather than asthma severity. Monitoring of exhaled NO may be useful in outpatient asthma management.