Table 1.

Theoretical versus actual defining criteria for the four early COPD status in current study.

Early COPD status	Theoretical criteria based on literatures and guidelines	Actual criteria used in this study
PRISm	People with post-bronchodilator FEV1/FVC ≥0.70 and FEV1 and/or FVC <80% predicted, or FEV1/FVC ≥ LLN and FEV1 < LLN.11, 12, 13	People with post-bronchodilator FEV1/FVC ≥0.70 and FEV1 and/or FVC <80% predicted, and not diagnosed as asthma.
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 CT emphysema, small and/or large airway impairments) and/or functional (e.g. low 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.14	People who presented with respiratory symptoms (including chronic cough, chronic sputum production, dyspnea, and/or exacerbation) and SAD but not diagnosed as COPD (i.e. post-bronchodilator FEV1/FVC ≥0.70) and asthma. (The SAD judging criteria were consistent with a prior analysis in the CPH study.15)
Young COPD	COPD patients with post-bronchodilator FEV1/FVC <0.70 diagnosed in the 20–50 year age range.7, 8, 9	COPD patients with post-bronchodilator FEV1/FVC <0.70 in the 20–50 year age range, and not diagnosed as asthma.
Mild COPD	COPD patients with post-bronchodilator FEV1/FVC <0.70 and FEV1 ≥ 80% predicted.7, 8, 9	COPD patients with post-bronchodilator FEV1/FVC <0.70 and FEV1 ≥ 80% predicted, and not diagnosed as asthma.

The four mutually exclusive early COPD status (i.e. PRISm, pre-COPD, young COPD, and mild COPD) were defined according to the latest Global Initiative for Chronic Obstructive Lung Disease reports and cutting-edge papers. COPD = chronic obstructive pulmonary disease. CPH = China Pulmonary Health. CT = computed tomography. DLco = diffusion capacity for carbon monoxide. FEV₁ = forced expiratory volume in 1 s. FVC = forced vital capacity. LLN = lower limit of normal. PRISm = preserved ratio impaired spirometry. SAD = small airway dysfunction.