Impact of subsidized health insurance coverage on emergency department utilization by low-income adults in Massachusetts

Background: In 2006, Massachusetts expanded insurance coverage to many low-income individuals. Objectives: This study aimed to estimate the change in emergency department (ED) utilization per individual among a cohort who qualified for subsidized health insurance following the Massachusetts health care reform. Research Design: We obtained Massachusetts public health insurance enrollment data for the fiscal years 2004-2008 and identified 353,515 adults who enrolled in Commonwealth Care, a program that subsidizes insurance for low-income adults. We merged the enrollment data with statewide ED visit claims and created a longitudinal file that indicated each enrollee's ED visits and insurance status each month during the preenrollment and postenrollment periods. Measures: We estimated the ratio in an individual's odds of an ED visit during the postperiod versus preperiod by conditional logistic regression. Results: Among the 112,146 CommCare enrollees who made at least 1 ED visit during the study period, an individual's odds of an ED visit decreased 4% [odds ratio (OR) = 0.96; 95% confidence interval (CI), 0.94, 0.98] postenrollment. However, it varied significantly depending on preenrollment insurance status. A person's odds of an ED visit was 12% higher in the postperiod among enrollees not publicly insured prior (OR = 1.12; 95% CI, 1.10, 1.25), but was 18% lower among enrollees who transitioned from the Health Safety Net, a program that pays for limited services for lowincome individuals (OR = 0.82; 95% CI, 0.78, 0.85). Conclusions: Expanding subsidized health insurance did not uniformly change ED utilization for all newly insured low-income adults in Massachusetts.