LAUSR

Supplemental Digital Content is available in the text. Background: Accountable Care Organizations (ACOs) have proliferated after the passage of the Affordable Care Act in 2010. Few longitudinal ACO studies with continuous enrollees exist and most are short term. Objective: The objective of this study was to evaluate the long-term impact of a commercial ACO on health care spending, utilization, and quality outcomes among continuously enrolled members. Research Design: Retrospective cohort study design and propensity-weighted difference-in-differences approach were applied to examine performance changes in 2 ACO cohorts relative to 1 non-ACO cohort during the commercial ACO implementation in 2010–2014. Subjects: A total of 40,483 continuously enrolled members of a commercial health maintenance organization from 2008 to 2014. Measures: Cost, use, and quality metrics for various type of services in outpatient and inpatient settings. Results: The ACO cohorts had (1) increased inpatient and outpatient total spending in the first 2 years of ACO operation, but insignificant differential changes for the latter 3 years; (2) decreased outpatient spending in the latter 2 years through reduced primary care visits and lowered spending on specialists, testing, and imaging; (3) no differential changes in inpatient hospital spending, utilization, and quality measures for most of the 5 years; (4) favorable results for several quality measures in preventive and diabetes care domains in at least one of the 5 years. Conclusions: The commercial ACO improved outpatient process quality measures modestly and slowed outpatient spending growth by the fourth year of operation, but had a negligible impact on inpatient hospital cost, use, and quality measures.