A study of fraction of exhaled nitric oxide levels as a diagnostic marker in patients with bronchial asthma

Aim: To compare the fraction of exhaled nitric oxide (FENO) levels in patients with and without bronchial asthma and correlate the FENO level with steroid therapy and severity of bronchial asthma.Study design: A cross-sectional case control study of 55 cases of bronchial asthma and 45 controls.Materials and methods: Fifty-five cases of bronchial asthma and 45 controls with identical demographic characteristics, having respiratory diseases other than asthma but not on steroids were studied and compared. Computerised spirometry studies and FENO levels measurement by chemiluminiscence NO-analyser was performed in both the groups and compared. The data was analysed using SPSS software.Results: The mean FENO levels were significantly higher in asthmatics [16.5 parts per billion (ppb)] as compared to non asthmatics (5.5 ppb). The sensitivity of FENO in making a diagnosis of asthma was 72% and the specificity 88%. The mean FENO levels were significantly higher in both steroid treated cases (15.7 ppb) and steroid naïve cases (41.5 ppb) as compared to controls (14.4 ppb). The mean FENO level increases as the severity of asthma increases in both steroid treated (mild-6.3, moderate-15.1, severe-18.8 ppb) and steroid naïve cases (mild-11.9, moderate-20.7, severe 28.9 ppb). The FENO levels were lower in steroid treated cases as compared to steroid naïve cases, however the difference was not statistically significant. Conclusion: FENO levels are elevated in bronchial asthma and have a sensitivity of 72% and specificity of 88% as a diagnostic marker. FENO levels significantly correlate with the severity of asthma and the levels reduce with steroid therapy.