Temporal Associations and Heterogeneity of Diagnosis-Related Group (DRG) Payment Reform with Hospitalization Costs Among Patients with Colorectal Cancer in China.

Background/Objectives: We aimed to evaluate the temporal associations and heterogeneous patterns between the Beijing Diagnosis-Related Group (DRG) 2.0 payment reform and hospitalization costs and resource utilization among patients receiving major colorectal cancer (CRC) surgery and to explore hospital adaptive cost adjustment behaviors under bundled payment constraints. Methods: Utilizing inpatient data of 1232 colorectal cancer surgical patients from a Beijing hospital spanning January 2021 to October 2024, we adopted segmented regression interrupted time-series analysis (ITSA), with April 2022 defined as the policy intervention point. The analysis used total hospitalization expenses, itemized costs, cost composition proportions, and length of stay (LOS) as outcome indicators, conducted heterogeneity analysis, and applied seasonal autoregressive integrated moving average (SARIMA) counterfactual forecasting as a supplementary sensitivity check. All medical expenditures were inflation-adjusted based on Beijing's medical consumer price index (CPI), with 2024 as the base year. Results: After DRG implementation, total hospitalization costs showed an immediate decrease of 13,111.73 CNY and a sustained monthly downward trend of 1312.60 CNY. Medical consumable fees were the main component associated with total-cost reduction, and their proportion declined immediately by 4.1 percentage points. LOS showed no abrupt immediate decline but shortened by 0.22 days per month over the post-reform period. Heterogeneous association patterns were observed across selected clinical and treatment subgroups. SARIMA counterfactual forecasting provided supplementary, directional sensitivity evidence for the primary outcomes and was interpreted cautiously for volatile sub-item expenditures. Conclusions: DRG 2.0 reform was associated with lower hospitalization costs and improved bed-turnover efficiency among CRC surgical patients, mainly through reductions in consumable expenditures.