Association between physician-hospital integration and inpatient care delivery in accountable care organizations: An instrumental variable analysis

Objective: To investigate the relationship between physician-hospital integration within accountable care organizations (ACOs) and inpatient care utilization and expenditure. Data Sources: The primary data were Massachusetts All-Payer Claims Database (2009-2013). Study Setting: Fifteen provider organizations that entered a commercial ACO contract with a major private payer in Massachusetts between 2009 and 2013. Study Design: Using an instrumental variable approach, the study compared inpatient care delivery between patients of ACOs demonstrating high versus low integration. We measured physician-hospital integration within ACOs by the proportion of primary care physicians in an ACO who billed for outpatient services with a place-of-service code indicating employment or practice ownership by a hospital. The study sample comprised non-elderly adults who had continuous insurance coverage and were attributed to one of the 15 ACOs. Outcomes of interest included total medical expenditure during an episode of inpatient care, length of stay (LOS) of the index hospitalization, and 30-day readmission. An inpatient episode was defined as 30, 45, and 60 days from the admission date. Data Collection/Extraction Methods: Not applicable. Principal Findings: The study examined 33,535 admissions from patients served by the 15 ACOs. Average medical expenditure within 30 days of admission was $24,601, within 45 days was $26,447, and within 60 days was $28,043. Average LOS was 3.5 days, and 5.4% of patients were readmitted within 30 days. Physician-hospital integration was associated with a 10.6% reduction in 30-day expenditure (95% CI, -15.1% to -5.9%). Corresponding estimates for 45 and 60 days were - 9.7% (95%CI, -14.2% to -4.9%) and - 9.6% (95%CI, -14.3% to -4.7%). Integration was associated with a 15.7% decrease in LOS (95%CI, -22.6% to -8.2%) but unrelated to 30-day readmission rate. Conclusions: Our instrumental variable analysis shows physician-hospital integration with ACOs was associated with reduced inpatient spending and LOS, with no evidence of elevated readmission rates.