Association of DRG-based payment reform with inpatient costs and resource use among older adults: an interrupted time series study in a county-level referral hospital in China.

Background: China has rapidly expanded its diagnosis-related group (DRG)-based payment reform; however, evidence primarily focuses on urban pilots or specific disease cohorts. There is limited understanding of how DRG implementation affects out-of-pocket (OOP) spending, cost composition, and resource utilization among older adults treated in county-level referral hospitals. Methods: We conducted a retrospective interrupted time series study utilizing administrative inpatient data from a tertiary county-level referral hospital in eastern China. From July 1, 2021, to July 31, 2025, we identified 154,744 admissions among adults aged ≥60. The outcomes assessed included total costs, out-of-pocket costs, drug costs, material costs, examination/laboratory costs, and length of stay (LOS). The primary analysis used admission-level segmented regression with standard errors clustered by calendar month. Supplementary analyses used monthly aggregated models with Newey-West standard errors and exploratory disease-group heterogeneity analyses. Results: In the adjusted admission-level interrupted time series models, the implementation of DRG was associated with an immediate reduction in OOP costs ( Conclusion: Among older adult inpatients in a county-level referral hospital in China, DRG-based payment reform was associated with lower patient OOP but longer hospital stays. Its effects on total spending and cost composition were less consistent and varied across disease groups.