• Vishal Anand Shetty, Laura B Balzer, Kimberley H Geissler, and David L Chin.
• Department of Health Policy and Promotion, University of Massachusetts Amherst, Amherst.
• JAMA Netw Open. 2019 Jul 3; 2 (7): e196796.

ImportanceAccountable care organizations (ACOs) aim to control health expenditures while improving quality of care. Primary care has been emphasized as a means to reduce spending, but little is known about the implications of using specialists for achieving this ACO objective.ObjectiveTo examine the association between ACO-beneficiary office visits conducted by specialists and the cost and utilization outcomes of those visits.Design, Setting, And ParticipantsThis cross-sectional study obtained data on 620 distinct ACOs from the Centers for Medicare & Medicaid Services Shared Savings Program Accountable Care Organizations Public-Use Files from April 1, 2012, to September 30, 2017. Generalized estimating equation models were used for analysis of ACOs, adjusting for ACO-beneficiary health status, Medicare enrollment groups, ACO size, and proportion of participating specialists.ExposuresSpecialist encounter proportion, the percentage of office visits provided by a specialist, was categorized into 7 discrete groups: less than 35%, 35% to less than 40%, 40% to less than 45% (reference group), 45% to less than 50%, 50% to less than 55%, 55% to less than 60%, and 60% or greater.Main Outcomes And MeasuresThe primary outcome was total expenditures (given in US dollars) per assigned beneficiary person-year. The secondary outcomes were total numbers of emergency department visits, hospital discharges, skilled nursing facility discharges, and magnetic resonance imaging orders.ResultsIn total, the data set included 1836 ACO-year (number of participation years per ACO) observations for 620 distinct ACOs. Those ACOs with a specialist encounter proportion of 40% to less than 45% had $1129 (95% CI, $445-$1814) lower per-beneficiary person-year spending than did ACOs in the lowest specialist encounter proportion group and had $752 (95% CI, $115-$1389) lower per-beneficiary person-year spending compared with ACOs in the highest specialist encounter proportion group. Monotonic decreases in emergency department visits, hospital discharges, and skilled nursing facility discharges were observed with increasing specialist encounter proportion. Conversely, monotonic increases in magnetic resonance imaging volume discharges were observed with increasing specialist encounter proportion.Conclusions And RelevanceThese findings suggest that an ACO's ability to reduce spending may require sufficient involvement in care processes from specialists, who seem to complement the intrinsic primary care approach in ACOs.

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