Preserved ratio impaired spirometry (PRISm)

People with post-bronchodilator forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) ≥ 0.70 and FEV1 and/or FVC \< 80% predicted, or FEV1/FVC ≥ lower limit of normal (LLN) and FEV1 \< LLN.

COPD Stage 0

People who had COPD-related risk factor exposure (e.g. cigarette smoke) and/or presented with respiratory symptoms (e.g. chronic cough, and/or sputum production) whereas with normal pulmonary function.

Pre-COPD

People (importantly, of any age) who had respiratory symptoms (e.g. cough, sputum production, dyspnea, and/or exacerbation) with or without detectable structural (e.g. thoracic computed tomography (CT) emphysema, small and/or large airway impairments) and/or functional (e.g. low diffusion capacity for carbon monoxide (DLCO), hyperinflation, small airway obstruction, and/or accelerated FEV1 decline) abnormalities, in the absence of airflow limitation, and who might (or not) develop persistent airflow limitation (i.e. COPD) over time.

Early COPD

People who were younger than 50 years with ten or more pack-years smoking history and any of these abnormalities: i) early airflow limitation (post-bronchodilator FEV1/FVC \< LLN), ii) compatible thoracic CT abnormalities, iii) rapid decline in FEV1 (\> 60 ml/year) that was accelerated relative to FVC.

Young COPD

COPD patients with post-bronchodilator FEV1/FVC \< 0.70 diagnosed in the 20-50 year age range.

Mild COPD

COPD patients with post-bronchodilator FEV1/FVC \< 0.70 and FEV1 ≥ 80% predicted.

Controls

People who were not belonged to any of above six early COPD status, and with pre- and post-bronchodilator FEV1/FVC ≥ 0·70, and with post-bronchodilator FEV1/FVC ≥ LLN.