INTRODUCTION: Measurement of fractional exhaled nitric oxide (FeNO) is a simple, noninvasive, reproducible, and convenient method for assessing airway inflammation. We here assessed the value of FeNO for distinguishing asthma-COPD overlap syndrome (ACOS) and chronic obstructive pulmonary disease (COPD) in patients hospitalized due to exacerbation of COPD.
METHODS: A total of 100 consecutive patients diagnosed with COPD and hospitalized due to disease exacerbation were included and divided into the COPD-alone group and ACOS group. FeNO was measured at the beginning of hospitalization and at discharge.
RESULTS: There was no correlation between FeNO values measured at the time of hospitalization and hospital duration (r = −0.10, P = 0.334). However, the mean FeNO value at the beginning of hospitalization was significantly higher in the ACOS group than in the COPD-alone group (25.5 [11–149] vs. 13.0 [5–50]; P < 0.001). The initial FeNO value was a good predictor of ACOS, with an optimum value of 18.5 parts per billion (sensitivity, 80%; specificity, 80%; positive and negative predictive values, 63.6% and 90.6%, respectively).

CONCLUSION: The FeNO level can identify ACOS in patients hospitalized for COPD exacerbation, providing a new diagnostic tool for the clinical management of ACOS and COPD.