METHODS: Cross sectional study was conducted by recruiting obstructive airway disease patients in outpatient clinic. Spirometry, including bronchodilator reversibility, skin prick test (SPT) and allergens specific IgE (sIgE) were done. Serum total IgE, exhaled nitric oxide (FeNO) and blood eosinophils were measured. HRCT was performed. History of tobacco smoking, pollution, biomass exposure and symptoms control score (ACT and CAT) were assessed. Patients were classified pure asthma, pure COPD and ACOS according to predefined definition of this study.