Mortality risk attributable to classification of chronic obstructive pulmonary disease and reduced lung function: A 21-year longitudinal cohort study

Aim: The mortality risk attributable to the classifications of chronic obstructive pulmonary disease (COPD) remains unclear. We investigated the associations of mortality with COPD classifications and reduced lung function in a large longitudinal cohort in Taiwan. Methods: A total of 388,401 adults (≥25 years of age) were recruited between 1996 and 2016 underwent 834,491 medical examinations including spirometry. We used the Global Initiative for Chronic Obstructive Lung Disease (GOLD) to establish the COPD classifications. A time-dependent Cox regression model was used to investigate the associations between the morality risk and COPD classifications. We also examined the associations between mortality and lung function. Results: The mean age of the participants was 42.1 years, and the median follow-up duration was 16.2 years. We identified 28,283 natural-cause deaths, and the mortality rate was 4.7 per 1,000 person-years. The hazard ratios (HRs) [95%confidence interval (95%CI)] of mortality in the participants with restrictive spirometry pattern and COPD GOLD Ⅰ–Ⅳ were 1.31 (1.27–1.35), 1.18 (1.00–1.39), 1.43 (1.35–1.51), 1.78 (1.66–1.90), and 2.13 (1.94–2.34), respectively, with reference to the participants with normal lung function. The natural-cause mortality risk increased by 33% [HR(95%CI): 1.33 (1.28–1.39)] for participants with COPD. Reduced lung function was also associated with a higher mortality risk. Conclusions: A more advanced classification of COPD was associated with a greater increase in the mortality risk. Our study suggests that early detection of COPD and slowing the disease progress in patients with COPD are crucial for mortality prevention.