Changes in specialty care use and leakage in Medicare accountable care organizations.

OBJECTIVES: Reducing leakage to outside specialists has been promoted as a key strategy for accountable care organizations (ACOs). We sought to examine changes in specialty care leakage and use associated with the Medicare Shared Savings Program (MSSP). STUDY
DESIGN: Analyses of trends in ACOs from 2010 to 2014 and quasi-experimental difference-in-differences analyses comparing changes for ACOs versus local non-ACO providers from before until after the start of ACO contracts, stratified by ACO specialty composition and year of MSSP entry.
METHODS: We used Medicare claims for a 20% sample of beneficiaries attributed to ACOs or non-ACO providers. The main beneficiary-level outcome was the annual count of new specialist visits. ACO-level outcomes included the proportion of visits for ACO-attributed patients outside of the ACO (leakage) and proportion of ACO Medicare outpatient revenue devoted to ACO-attributed patients (contract penetration).
RESULTS: Leakage of specialist visits decreased minimally from 2010 to 2014 among ACOs. Contract penetration also changed minimally but differed substantially by specialty composition (85% for the most primary care-oriented quartile vs 47% for the most specialty-oriented quartile). For the most primary care-oriented quartile of ACOs in 2 of 3 entry cohorts, MSSP participation was associated with differential reductions in new specialist visits (-0.04 visits/beneficiary in 2014 for the 2012 cohort; -5.4%; P <.001). For more specialty-oriented ACOs, differential changes in specialist visits were not statistically significant.
CONCLUSIONS: Leakage of specialty care changed minimally in the MSSP, suggesting ineffective efforts to reduce leakage. MSSP participation was associated with decreases in new specialty visits among primary care-oriented ACOs.