The results of this study show that the measurement of FENO50
may be more useful than a bronchodilator test in the diagnosis of
COPD phenotype in patients who receive assistance at a respiratory
clinic, with an optimal cut-off value of 19 ppb. Although this levels
are in the normal range for the general population [23], data on
FENO distribution in COPD patients are scarce and could not be
extrapolated from general population.