These results may be helpful in the diagnosis of ACOS when it
comes to replacing a test that is not habitually available in most
centers, such as sputum eosinophilia. Although in various studies
the latter was associated with FENO50 and its response to ICS [19],
these results have not been validated in this population of ACOS.
Furthermore, although blood eosinophilia could be a good marker
of ICS response in terms of exacerbation prevention [31], to date no
data exists comparing blood eosinophils and FENO50 in COPD.