County-Level Variation in Emergency Department Admission Rates Among US Medicare Beneficiaries

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Study objective:

Hospital-based emergency departments (EDs) are the gateway to hospital admissions for many Americans. Approximately half of all US hospital admissions originate from EDs, and more than 3 in 4 are among Medicare beneficiaries. Recent literature has demonstrated nearly 2-fold variation in both physician- and hospital-level ED admission rates. We study geographic variation at the county level in ED admission rates among Medicare fee-for-service beneficiaries.


Using the 100% population data from the Centers for Medicare & Medicaid Services (CMS), we analyzed beneficiaries continuously enrolled in Medicare fee-for-service Parts A and B who resided in the 50 states and the District of Columbia in 2012. The ED admission rate was aggregated to the county level. ED admission rates were adjusted with the CMS Hierarchical Condition Categories (HCC) risk score. The resulting HCC adjusted ED admission rate was mapped to display the variation by county.


The average county HCC adjusted ED admission rate was 30.8% in the Medicare population. Counties in the lowest quintile had an ED admission rate of 19.9% or lower. By comparison, counties in the highest quintile had an ED admission rate of 40.3% or higher.


Among Medicare beneficiaries, county-level ED admission rates varied 2-fold between counties in the lowest and highest quintiles. Future work should focus on exploring causes for this variation, such as racial ethnic composition, socioeconomic status, and health care delivery system characteristics and the research of effectiveness of policies that affect ED admission decisions.

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