Abstract
Emergency and acute hospital services in England are under increasing pressure. The aim of this study was to investigate the association between key case-mix indicators and outcomes for adults admitted to hospital with an acute medical condition in England. All patients aged ≥16 years admitted to hospital in England as an acute unselected medical admission and who survived to discharge during the financial year 2021-2022 were included. Length of hospital stay was the primary outcome of interest. Data were available for 1,586,168 unique patients. A case-mix index was developed with a score that ranged from 0 to 12. Frailty was the most important variable in the index, followed by multiple health conditions and patient age. The mean case-mix score across hospital trusts in England ranged from 5.3 to 7.8. The case-mix index will support initiatives to better understand factors contributing to outcomes from acute medical admissions to hospital.