SERPING1 and chronic obstructive pulmonary disease: Longitudinal analyses in the UK Biobank (n = 46,369) and ECOPD cohort (n = 576) revealed that higher circulating SERPING1 protein levels were causally linked to slower FEV1 decline during early follow-up (UKB: adjusted difference = –22.1 mL/year per standardized unit; ECOPD: –0.73 mL/year per ng/mL), accompanied by marked expression differences between European (higher) and Asian (lower) smokers and COPD patients.