Fractional exhaled nitric oxide in chronic obstructive pulmonary disease

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Background: Fractional exhaled Nitric Oxide concentration (FeNO) is a measure of airway inflammation. It is being used increasingly in asthma as a biomarker for eosinophilic airway inflammation and response to corticosteroid therapy. However, there is comparatively little work examining FeNO in patients with chronic obstructive pulmonary disease (COPD). Up to 30% of patients with COPD have a significant eosinophilic driver to their disease. Furthermore, evidence suggests cigarette smoke may artefactually reduce the concentration of exhaled nitric oxide. We examine whether FeNO values are affected by smoking and whether FeNO levels are predictive of eosinophilic or neutrophilic subtypes in COPD. Methods: FeNO was measured in 84 stable patients with COPD GOLD stage 1-4 and without prior diagnosis of asthma. Results: There was a statistically significant difference in FeNO values between those who smoked and those who didn9t (14.7 v 22.2, p=0.0065). There was no observable correlation between FeNO and sputum eosinophil count (r=0.02) or blood eosinophil count (r=0.07). There was no observed correlation between FeNO and the presence or absence of sputum microbiota (mean FeNO 23.1 v 20.0, p=0.44). Conclusion: In COPD FeNO is significantly lower in patients who continue to smoke. However, unlike asthma, in patients with COPD high FeNO does not appear to predict high sputum or blood eosinophil levels, nor is there a correlation between FeNO and sputum mibrobiota. FeNO, therefore, does not appear helpful in typing COPD patients into eosinophilic or neutrophilic subtypes in the stable state. We await data to determine whether FeNO varies in exacerbations, and whether it will be useful in predicting treatment response.