Exhaled nitric oxide reflects asthma severity and asthma control

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Abstract
This study was undertaken to a) evaluate whether exhaled nitric oxide (fraction of exhaled nitric oxide [FENO]) levels are reflective of asthma severity in concordance with the National Asthma Education and Prevention Program categorization and b) determine the usefulness of FENO using the single-breath exhalation technique for monitoring asthma control and compliance with steroid treatment. Thirty patients with asthma (7-17 yrs old; 14 males and 16 females) that was mild (n=8), moderate (n=17), or severe (n=5) were included in the study. Fifteen patients were seen on more than one occasion for a total of 53 visits. Information obtained at each visit included asthma symptoms, beta-agonists and corticosteroids use, compliance to steroids, and forced expiratory volume in 1 sec (FEV1) and FENO measurements. Asthma control was judged by a pulmonologist based on overall evaluation of symptoms, FEV1 measurements, and the frequency of beta-agonists use at each visit. The mean +/- SD FENO was significantly different in the mild, moderate, and severe asthma categories (30 +/- 12, 65 +/- 48, 104 +/- 68, respectively; F(2,52)=6.02 p=.005). FENO was significantly correlated with asthma severity (r=.44, p=.001), compliance (r=-.75, p=.001), and control (r=-.51, p=.001). There were no statistically significant differences between asthma severity and compliance or FEV1. Our data suggest that a) FENO may be a practical tool to evaluate asthma severity and asthma control over time and b) FENO may be used as a marker of compliance with steroids even when FEV1 has not decreased significantly.