Longitudinal Spirometric Trajectory from Normal Lung Function to PRISm and COPD in a Population-Based Korean Cohort

Background: Chronic obstructive pulmonary disease (COPD) develops through heterogeneous lung-function trajectories, but the longitudinal role of preserved ratio impaired spirometry (PRISm) in progression toward COPD remains unclear. Objective: We aimed to characterize long-term spirometric trajectories and transitions from normal spirometry to PRISm or COPD in a population-based cohort. Patients and Methods: We analyzed data from the Ansan–Ansung cohort of the Korean Genome and Epidemiology Study. Among medication-free participants with normal baseline spirometry who had classifiable spirometry across seven examinations over approximately 12 years, longitudinal trajectories of forced expiratory volume in 1 second (FEV 1 , % predicted) and the FEV 1 /FVC ratio were evaluated. Participants were classified into normal maintenance, PRISm, or COPD trajectory groups using a clinically interpretable, rule-based approach. Because post-bronchodilator measurements were not available across all examinations, COPD was operationally defined using pre-bronchodilator spirometry as FEV 1 /FVC < 0.70. Results: Lung-function decline followed heterogeneous trajectories rather than a single linear pathway. Among 1,753 participants, 1,658 (94.6%) remained normal, 21 (1.2%) developed PRISm, and 74 (4.2%) progressed to COPD. Most individuals who developed COPD did so without a preceding sustained PRISm phase. In descriptive baseline comparisons, the COPD trajectory showed greater smoking exposure, higher blood pressure, and more pronounced central adiposity, whereas PRISm was more closely associated with wheeze-related respiratory symptoms and lower baseline lung function. In multivariable logistic regression, older age and current smoking were the strongest independent predictors of progression to COPD. Conclusion: Progression toward COPD in the general population is heterogeneous, and PRISm is not an obligatory precursor to COPD. Longitudinal spirometric assessment may provide clinically relevant insights beyond single time-point classification in the general population. Plain Language Summary: Why was the study done? COPD does not develop in the same way in everyone. Preserved ratio impaired spirometry (PRISm) has been proposed as an early stage of COPD, but its long-term role remains uncertain. This study examined how lung function changes over time and whether PRISm always leads to COPD. What did the researchers do? We studied Korean adults from the general population who had normal lung function at baseline. Lung function was measured seven times over about 12 years using spirometry. We tracked each person’s lung-function pattern over time and grouped participants according to their long-term trajectories. What did the researchers find? Lung-function change was heterogeneous. Most participants remained normal, some developed PRISm, and a smaller group developed COPD. Many individuals who developed COPD did so without a sustained PRISm phase. The COPD trajectory was more strongly associated with older age and smoking, and descriptively showed less favorable baseline clinical profiles, whereas PRISm was more closely associated with wheeze-related symptoms and lower baseline lung function. What do these results mean? PRISm is not always a necessary step before COPD. Repeated spirometry over time may provide more useful information than a single test for identifying people at risk of COPD and for understanding different pathways of disease development. Keywords: COPD, PRISm, KoGES, longitudinal study, spirometry