Changes in Hospital Malnutrition Coding Following Diagnosis-Related Group Payment Reform: Evidence From a Chinese Tertiary Hospital.

RATIONALE: Malnutrition remains systematically undercoded in hospital administrative records, despite its high prevalence among patients with non-communicable diseases (NCDs). China's Diagnosis-Related Group (DRG) payment reform links reimbursement to secondary diagnosis coding, potentially incentivising changes in clinical documentation. AIMS AND OBJECTIVES: This study evaluates the validity of administrative malnutrition coding and its association with clinical outcomes in the context of DRG reform. METHOD: A retrospective cross-sectional study was conducted using administrative data from a tertiary hospital in southwest China (2023-2025), including 31,133 inpatient admissions with a primary NCD diagnosis. Patients were categorised by insurance type: Urban and Rural Residents' Basic Medical Insurance (URRBMI) or Urban Employees' Basic Medical Insurance (UEBMI). Multivariable logistic regression was used to identify predictors of malnutrition coding and estimate associations with in-hospital mortality and prolonged hospitalisation (LOS > 10 days), adjusting for age, insurance, admission route, and primary diagnosis. RESULTS: The prevalence of coded malnutrition was 8.5%, surging from 5.3% in 2023% to 11.0% in 2024 before stabilizing at 9.2% in 2025. After case-mix adjustment, the year of admission remained a significant predictor (2024: OR = 2.23; 2025: OR = 1.71). Coded malnutrition independently predicted in-hospital mortality (OR = 4.35) and prolonged hospitalisation (OR = 1.32). URRBMI patients consistently demonstrated higher coding rates, while the association between malnutrition coding and mortality was stronger in UEBMI patients. CONCLUSION: Malnutrition coding increased markedly following DRG reform. The robust association with adverse clinical outcomes validates these codes as meaningful markers of nutritional risk. Our findings underscore the need for systematic nutritional screening in hospital admission protocols to ensure equitable and clinically accurate reimbursement.