Early Functional Impairment in Smokers with CT-Detected Emphysema: Spirometry Provides Complementary Physiological Information in Lung Cancer Screening

Background: Low-dose computed tomography (LDCT) lung cancer screening (LCS) frequently identifies emphysema in high-risk smokers. However, the extent to which CT-detected emphysema reflects underlying physiological impairment remains uncertain. We evaluated whether spirometry can detect functional abnormalities in this population beyond structural imaging findings. Methods: This cross-sectional study included 323 individuals with LDCT- detected emphysema and no lung cancer or prior chronic respiratory diseases within a screening cohort (n = 3076). Participants underwent pre-bronchodilator spirometry and symptom assessments (COPD Assessment test (CAT) and Modified Medical Research Council (mMRC) Dyspnea Scale). Pre-bronchodilator airflow limitation was defined as forced expiratory volume in one second to forced vital capacity ratio (FEV1/FVC) < 0.70. Small airways dysfunction was defined by ≥2 reduced mid-expiratory flow parameters (<60% predicted). Flow–volume curve morphology was assessed qualitatively. Results: Pre-bronchodilator airflow limitation was observed in 45.2% of participants, predominantly mild. Small-airway dysfunction was present in 52%, and an abnormal flow–volume curve morphology in 67.5%. Notably, functional abnormalities were frequently observed despite preserved FEV1. Symptom burden was low, with only 7.7% of participants reporting clinically significant symptoms. Functional impairments often overlapped and were common in minimally symptomatic individuals. Conclusions: In a lung cancer screening (LCS) cohort with CT-detected emphysema, functional abnormalities are frequently observed, including in individuals with preserved FEV1 and minimal symptoms. Spirometry provides additional physiological insight beyond structural imaging; however, these findings are descriptive and should not be interpreted as diagnostic of COPD. Further studies are needed to determine their clinical relevance.