Study Population
Subjects were recruited by their family physicians from
14 health-care centers in rural areas of Xuzhou City, China, from January to March 2008. At baseline, the subjects had to have a diagnosis of COPD according to the criteria proposed by the Global Initiative for Chronic Obstructive Lung Disease (GOLD). The following exclusion criteria were used to minimize selection bias by the County People’s Hospital: presence of fever, active tuberculosis, changes in radiographic images or medication in the 4 weeks immediately preceding recruitment, primary diagnosis of asthma or obvious bronchiectasis, cystic fibrosis, interstitial lung disease, previous lung-volume-reduction surgery, lung transplantation, pneumonectomy, uncontrolled or serious conditions that could potentially affect spirometry tests, and refusal to fill out psychological
questionnaires. The subjects completed questionnaires and underwent spirometry testing at both the baseline assessment and at the end of the follow-up assessments. General characteristics were documented based on subject reports. Weight and height were measured before pulmonary function
tests were conducted. All qualified candidates were
invited to participate in the study during home visits. All
subjects were of Han ancestry and had the same cultural background and dietary habits. The subjects underwent follow-up interviews with questionnaires and spirometry tests in the same health-care centers for both baseline and follow-up surveys. The end points were the last follow-up results of each subject. Subjects were lost to follow-up if we could not contact them or if they moved to another location, withdrew consent, refused to proceed, had invalid data, or were unable to complete the study.