Inclusion and exclusion criteria

The research protocol complied with the principles of the Declaration of Helsinki and was approved by the Ethics Committee of the West China Hospital of Sichuan University of the People’s Republic of China. All subjects provided written informed consent. From January to December 2016, the healthy volunteers, COPD patients and those with exacerbation of COPD were recruited at the hospital outpatient and inpatient departments of West China Hospital of Sichuan University. All patients were previously diagnosed with COPD based on GOLD documents. All subjects were asked about their medical history in detail, and chest CTs from the most recent year were reviewed. Exclusion criteria were as follows: 1) suffering from diseases other than COPD or acute exacerbation of chronic obstructive pulmonary disease (AECOPD), 2) unable or unwilling to cooperate with a doctor, 3) unable or unwilling to perform lung function tests, and 4) suffering from pulmonary diseases (acute respiratory distress syndrome [ARDS], asthma and lung cancer) or other diseases known to affect plasma endocan (including tumors, atherosclerosis and chronic kidney disease).