Abstract:Objective To explore the value of exhaled nitric oxide (FeNO) in the diagnosis and treatment of in asthma-chronic obstructive pulmonary disease overlap syndrome(ACO). Methods A total of 171 patients were enrolled in this study, including 44 patients with asthma, 86 patients with chronic obstructive pulmonary disease (COPD) and 41 patients with ACO. 45 healthy subjects were selected as the control group. The differences of clinical characteristics, peripheral blood indexes, FeNO and pulmonary function include maximum expiratory volume in the first second (FEV1), forced vital capacity (FVC), maximum expiratory volume in the first second/ predicted value (FEV1% pred), maximum expiratory volume in the first second/forced vital capacity(FEV1/FVC) among the four groups were analyzed. And the relationship between FeNO and pulmonary function, peripheral blood indexes was analyzed. Results The age composition of asthma group was lower than that of COPD group and ACO group (P < 0.05). The levels of EOS% in peripheral blood and FeNO of ACO group were lower than those in asthma group but higher than those in COPD group (P < 0.05). There was a positive correlation between FeNO and the level of EOS% in peripheral blood in ACO group and asthma group (r s = 0.383 and 0.316, P < 0.05). The levels of FEV1, FVC, FEV1/% pred, FEV1/FVC in COPD group and ACO group were lower than those in asthma group (P < 0.05). Conclusion FeNO and peripheral blood EOS% have important reference value for the diagnosis of ACO. Combination with pulmonary function is helpful in the diagnosis of ACO.