192 patients were studied: 103 with COPD; 16 healthy non-smokers; 30 healthy smokers; and
43 asthmatics. COPD patients were grouped by phenotype: 34 non exacerbators (33.0%); 22 ACOS
(21.3%); 13 frequent exacerbators with emphysema (12.6%); and 34 frequent exacerbators with chronic
bronchitis (33.0%). ACOS patients showed significantly higher FENO50 values compared to the others
after adjustments for confounding factors. FENO50 demonstrated greater diagnostic accuracy than the
bronchodilator test (BT) in the diagnosis of ACOS and COPD phenotypes (AUC 0.79 vs 0.74), with an
optimal cut-off value of 19 ppb (sensitivity 0.68, specificity 0.75)