Follow-up within 30 days of an emergency department (ED) visit for mental illness is a new and widely-used quality measure. However, no empirical evidence validates associations between follow-up and subsequent utilization based outcomes. Using Massachusetts all payer claims data, we identified insured individuals with an ED visit for mental illness. Multivariate regression analysis estimated associations between follow-up within 30 days after an ED visit for mental illness with costs, hospitalizations, and additional ED visits in 180 days following the index visit. 63,814 index ED visits were included (56.5% female, mean [SD] age 38.0 [12.1] years, 48% Medicaid covered). 31% of index ED principal diagnoses were for major depressive disorder, 3% schizophrenia, 5% bipolar disorder, 34% anxiety disorder, 0.6% post-traumatic stress disorder, 8% other psychoses, and 19% other mental illness diagnoses. Only 33% of patients had a follow-up visit for mental illness within 30 days. Adjusted regression analyses show timely follow-up is associated with increased costs in the 180 days after (average marginal effect = $1622; 95% confidence interval [CI] 1459, 1786), an increased probability of inpatient hospitalization (2.7 percentage points; 95% CI 0.021, 0.032), and a small reduction in the probability of at least one additional ED visit (- 1.7 percentage points; 95% CI - 0.026 to 0.009). Overall follow-up rates are low; follow-up within 30 days of an ED visit for mental illness is associated with increased costs and increased probability of hospitalization in the follow-up period. It is not known whether increased rates of utilization improve patient outcomes, potentially by receiving appropriate more intensive care.
Keywords: Emergency department use; Healthcare costs; Hospitalization; Mental illness.