Development of AECOPD Identification Tool (DETECT Study)

Inclusion Criteria: -≥ 40 years old of age. * Able to adequately understand written and verbal * A signed and dated written informed consent must be obtained prior to the visits * Patients see doctors due to suffering respiratory disease below: Disease type 1 - diagnosed moderate and severe stable COPD * Patients with a diagnosis of COPD and documented record with predicted ratio of FEV1 to forced vital capacity (FVC) \< 0.70 before the study visit * COPD with moderate to severe airflow obstruction (FEV1\<0.8 predicted) Disease type 2 - AECOPD * Patients with a diagnosis of COPD and documented record with predicted ratio of FEV1 to forced vital capacity (FVC) \< 0.70 before the study visit * Patients consult the clinic or the emergency department because of acute worsening with an AECOPD (diagnosed by more than 2 clinical experts and refer to diagnosis criteria of Appendix 2) Disease type 3 -Non-COPD patients with chronic respiratory symptoms such as cough, sputum and wheeze, dyspnea etc. (≥2 high risk factors ) Exclusion Criteria: * Patients with severe cardiovascular disease, including uncontrolled hypertension with drug treatment, unstable angina, myocardial infarction within the last 6 months, NYHA class II congestive heart failure, severe arrhythmia, pericardial effusion, etc. * Patients with lung cancer, esophageal cancer or mediastinal tumors; * Patients who participated in any drug clinical trials within 4 weeks before enrollment; * Patients with severe infection, indicated for intravenous antibiotics, antifungal or antiviral therapy; * Patients suffering from mental illness and poor compliance; * Patients inappropriate for inclusion decided by investigator.