The hospital emergency department (ED) plays a unique and important role in the American health sector and broader society. EDs are designed to treat the most critically ill and injured patients and they are part of the first response to public health emergencies such as natural disasters and terrorist attacks. In addition, EDs also serve as a bellwether of performance in other parts of the health care system. This synthesis describes what is known, and importantly what is not known, about hospital EDs in the United States. The authors address key questions about the performance and sustainability of hospital EDs and what patterns of ED utilization reveal about the functioning of the U.S. health sector overall.

The following questions are addressed in this synthesis:

1. What characteristics of patients and local health care systems are associated with ED utilization?
2. How frequently do patients use the ED for non-urgent or preventable conditions and what are the factors that influence this utilization?
3. How does patient cost-sharing affect ED utilization and health outcomes?
4. How do current ED utilization patterns affect hospital finances?
5. What are the causes and consequences of ED overcrowding?
6. What are the cost implications of ED utilization?

Implications for policy-makers:

• Expansion of health insurance coverage on its own is likely to increase rather than decrease stress on overcrowded EDs.
• Align reimbursement incentives to improve hospital patient flow and reduce ED overcrowding.
• Improve access to primary care, either through community providers or through delivery of primary care in the ED.