Effect of Attribution Length on the Use and Cost of Health Care for a Pediatric Medicaid Accountable Care Organization

IMPORTANCE: Little is known about the effect of pediatric accountable care organizations (ACOs) on the use and costs of health care resources, especially in a Medicaid population. OBJECTIVE: To assess the association between the length of consistent primary care (length of attribution) as part of an ACO and the use and cost of health care resources in a pediatric Medicaid population. DESIGN, SETTING, AND PARTICIPANTS: A retrospective study of Medicaid claims data for 28,794 unique pediatric patients covering 346,277 patient-attributed months within a single children's hospital. Data were collected for patients attributed from September 1, 2013, to May 31, 2015. The effect of the length of attribution within a single hospital system's ACO on the use and costs of health care resources were estimated using zero-inflated Poisson distribution regression models adjusted for patient characteristics, including chronic conditions and a measure of predicted patient use of resources. EXPOSURES: Receiving a plurality of primary care at an ACO clinic during the preceding 12 months (attribution to the ACO). MAIN OUTCOMES AND MEASURES: The primary outcome measure was the length of attribution at an ACO clinic compared with subsequent inpatient hospitalization and subsequent use and cost of outpatient and ancillary health care resources. RESULTS: Among the 28,794 pediatric patients receiving treatment covering 346,277 patient-attributed months during the study period, continuous attribution to the ACO for more than 2 years was associated with a decrease (95% CI) of 40.6% (19.4%-61.8%) in inpatient days but an increase (95% CI) of 23.3% (2.04%-26.3%) in office visits, 5.8% (1.4%-10.2%) in emergency department visits, and 15.3% (12.5%-18.0%) in the use of pharmaceuticals. These changes in the use of health care resources combined resulted in a cost reduction of 15.7% (95% CI, 6.6%-24.8%). At the population level, the impact of consistent primary care was muted by the many patients in the ACO having shorter durations of participation. CONCLUSIONS AND RELEVANCE: These findings suggest significant and durable reductions of inpatient use and cost of health care resources associated with longer attribution to the ACO, with attribution as a proxy for exposure to the ACO's consistent primary care. Consistent primary care among the pediatric Medicaid population is challenging, but these findings suggest substantial benefits if consistency can be improved.