Coordinating care across hospitals: how integration shapes patient mobility

BACKGROUND: In 2016, France reformed its health system by requiring public hospitals to form territorial groups. Policymakers, following experiences with integrated care provision in the United States and NHS-type networks in Italy and England, expected these groups to improve coordination and system efficiency. However, it remains unclear whether such administrative integration creates new care pathways within groups or substitutes for existing referral relationships with external providers. METHODS: We analyzed national hospital administrative data from 2013 to 2021. Changes in inter-facility transfer rates were estimated using a synthetic difference-in-differences approach. The main outcome was the annual percentage of patients transferred to another hospital, overall and within the same group. RESULTS: Following group formation, smaller local hospitals experienced an average increase of 1.25 percentage points in transfers to hospitals within their group. Transfers to hospitals outside the group remained broadly stable, suggesting limited substitution away from pre-existing referral channels. CONCLUSIONS: Territorial grouping are associated with an increase in internal patient mobility, particularly among local hospitals, without reducing exchanges with external providers. These findings suggest that administrative integration may have layered new coordination arrangements onto existing care pathways and reinforced patterns of functional specialization. The results contribute to understanding how network-based integration reshapes organizational behaviour and patient mobility in regulated health systems.