Emergency Severity Index
The Emergency Severity Index is a five-level emergency department triage algorithm, initially developed in 1999. It is maintained by the Agency for Healthcare Research and Quality.
ESI triage is based on the acuity of patients' health care problems and the number of resources their care is anticipated to require. This differs from standardized triage algorithms used in several other countries, such as the Australasian Triage Scale, which attempt to divide patients based on the time they may safely wait.
The concept of a "resource" in ESI means types of complex interventions or diagnostic tools, above and beyond physical examination. Examples of resources include X-ray, blood tests, sutures, and intravenous or intramuscular medications. Oral medications and prescriptions are specifically not considered resources by the ESI algorithm.
The ESI levels are numbered one through five, with level one indicating the greatest urgency. The levels are as follows:
| Level | Name | Description | Examples |
| 1 | Resuscitation | Immediate, life-saving intervention required without delay | Cardiac arrest Massive bleeding |
| 2 | Emergent | High risk of deterioration, or signs of a time-critical problem | Cardiac-related chest pain Asthma attack |
| 3 | Urgent | Stable, with multiple types of resources needed to investigate or treat | Abdominal pain High fever with cough |
| 4 | Less Urgent | Stable, with only one type of resource anticipated | Simple laceration Pain on urination |
| 5 | Nonurgent | Stable, with no resources anticipated except oral or topical medications, or prescriptions | Rash Prescription refill |