Incidental Emphysema on Health Screening Chest CT Imaging and All-Cause Mortality in a Korean Cohort

BACKGROUND:Incidental emphysema on health-screening chest CT imaging is common, yet its prognostic significance in asymptomatic populations is characterized poorly. RESEARCH QUESTION:Is incidental emphysema on health screening chest CT imaging independently associated with all-cause mortality? STUDY DESIGN AND METHODS:This retrospective cohort comprised 41,291 adults undergoing chest CT imaging during routine health checkups in Korea (2002-2019). Emphysema was a binary variable from structured radiology reports, and the primary outcome was all-cause mortality via national death registry linkage. The primary analysis was a complete-case Cox model adjusted for age, sex, BMI, and smoking status; sensitivity analyses used multiple imputation, ever-smoking restriction, scanner-era adjustment, a time-varying exposure, and competing risks models. RESULTS:Emphysema was present in 3,774 participants (9.1%), rising from 2.6% in those who had never smoked to 14.6% in those who current smoked; over a median of 8.5 years, 284 deaths occurred. Emphysema was associated with all-cause mortality in the designated complete-case analysis (hazard ratio [HR], 1.54; 95% CI, 1.05-2.25), among those who had ever smoked after pack-years adjustment (HR, 1.63; 95% CI, 1.09-2.43), and when exposure was updated at repeat imaging (HR, 1.69; 95% CI, 1.18-2.41). Full-cohort pack-years imputation was not significant (HR, 1.36; 95% CI, 0.97-1.91), diluted by those who had never smoked, among whom no participant with emphysema died. An exploratory cancer signal (HR, 2.25) was concentrated in lung cancer (13 events). Adding emphysema to a smoking-inclusive model improved discrimination by ≤ 0.004. INTERPRETATION:Among those who had ever smoked, incidental emphysema on screening chest CT imaging was associated with mortality after adjustment for pack-years of smoking, although residual confounding because of smoking intensity cannot be excluded. After smoking history is known, the report adds almost nothing to discrimination and should not be used alone to stratify prognosis; we did not address whether it should prompt evaluation for undiagnosed COPD. In the full screening population, the association did not reach significance, but with 284 deaths, one-half the number needed for 80% power, that result is inconclusive, rather than negative.