Substance Use, Homelessness, Mental Illness and Medicaid Coverage: A Set-up for High Emergency Department Utilization

Frequent users of emergency departments (ED) account for 21-28% of all ED visits nationwide. The objective of our study was to identify characteristics unique to patients with psychiatric illness who are frequent ED users for mental health care. Understanding unique features of this population could lead to better care and lower healthcare costs.

This retrospective analysis of adult ED visits for mental healthcare from all acute care hospitals in California from 2009-2014 used patient-level data from California's Office of Statewide Health Planning and Development. We calculated patient demographic and visit characteristics for patients with a primary diagnosis of a mental health disorder as a percentage of total adult ED visits. Frequent ED users were defined as patients with more than four visits in a 12-month period. We calculated adjusted rate ratios (aRR) to assess the association between classification as an ED frequent user and patient age, sex, payer, homelessness, and substance use disorder.

In the study period, 846,867 ED visits for mental healthcare occurred including 238,892 (28.2%) visits by frequent users. Patients with a primary mental health diagnosis and a co-occurring substance use diagnosis in the prior 12 months (77% vs. 37%, aRR [4.02], 95% confidence interval [CI] [3.92-4.12]), homelessness (2.9% vs 1.1%, odds ratio [1.35], 95% [CI] [1.27-1.43]) were more likely to be frequent users. Those covered by Medicare (aRR [3.37], 95% CI [3.20-3.55]) or the state's Medicaid program Medi-Cal (aRR [3.10], 95% CI [2.94-3.25]) were also more likely to be frequent users compared with those with private insurance coverage.

Patients with substance use disorders, homelessness and public healthcare coverage are more likely to be frequent users of EDs for mental illness. Substance use and housing needs are important factors to address in this population.