These results are similar to those published by other groups,
which showed a relationship between FENO50 and bronchodilator
response [24,25] and between FENO50 and the presence of bronchial
hyperresponsiveness, a fact that is considered the
distinguishing feature of bronchial asthma [16]. The optimal cut-off
value for the diagnosis of ACOS is similar to that described by other
researchers. Some [26] observed an average level of 20 ppb FENO50
in COPD patients with a previous diagnosis of bronchial asthma