Hospital Participation in Medicare ACOs: No Change in Admission Practices and Spending

AJMC August 19, 2025
Amber K. Sabbatini, MD, MPH, David B. Muhlestein, PhD, JD

Hospital accountable care organization (ACO) participation did not impact emergency department admission rates, length of stay, or costs, suggesting limited effectiveness in reducing spending for unplanned admissions and challenging hospital-led ACO cost-saving strategies.

ABSTRACT

Objectives: Hospital participation in accountable care organizations (ACOs)—Medicare’s signature alternative payment model—continues to grow despite mixed evidence on spending and quality. This study examines whether hospital ACO participation is associated with changes in emergency department (ED) admission practices, hospital length of stay (LOS), and spending for unplanned admissions.

Study Design: A difference-in-differences analysis of Medicare fee-for-service ED visits and hospitalizations (2008-2019).

Methods: Medicare claims were linked to ACO tracking data from Torch Insight to identify hospitals that joined an ACO between 2012 and 2017 (6 cohorts,...

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