Different Relationships between FNO and COPD Characteristics in Smokers and Ex-Smokers.

Exhaled nitric oxide (FNO) is a marker of type-2 inflammation in asthma and is used in its management. However, smokers and ex-smokers have lower FNO values, and the clinical use of FNO values in COPD patients is unclear. Therefore, we investigated if FNO had a relationship to different COPD characteristics in smoking and ex-smoking subjects. Patients with COPD ( = 533, 58% females) were investigated while in stable condition. Measurements of FNO, blood cell counts, IgE sensitisation and lung function were performed. Medication reconciliation was used to establish medication usage. Smokers ( = 150) had lower FNO 9 (8, 10) ppb (geometric mean, 95% confidence interval) than ex-smokers did ( = 383) 15 (14, 16) ppb,  < 0.001. FNO was not associated with blood eosinophil or neutrophil levels in smokers, but in ex-smokers significant associations were found ( = 0.23,  < 0.001) and ( = -0.18,  = 0.001), respectively. Lower FNO values were associated with lower FEV% predicted in both smokers ( = 0.17,  = 0.040) and ex-smokers ( = 0.20,  < 0.001). Neither the smokers nor ex-smokers with reported asthma or IgE sensitisation were linked to an increase in FNO. Ex-smokers treated with inhaled corticosteroids (ICS) had lower FNO 14 (13, 15) ppb than non-treated ex-smokers 17 (15, 19) ppb,  = 0.024. This was not found in smokers ( = 0.325). FNO is associated with eosinophil inflammation and the use of ICS in ex-smoking COPD subjects, but not in smoking subjects suggesting that the value of FNO as an inflammatory marker is more limited in smoking subjects. The association found between low FNO values and low lung function requires further investigation.