Emergency Severity Index

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The Emergency Severity Index (ESI) is a five-level emergency department triage algorithm, initially developed in 1999. It is maintained by the Agency for Healthcare Research and Quality (AHRQ).

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 (such as lab tests plus X-ray imaging) Abdominal pain
High fever with cough
4 Less Urgent Stable, with only one type of resource anticipated (such as only an X-ray, or only sutures) Simple laceration
Pain on urination
5 Nonurgent Stable, with no resources anticipated except oral or topical medications, or prescriptions Rash
Prescription refill


Gilboy N, Tanabe T, Travers D, Rosenau AM (2011). Emergency Severity Index (ESI): A Triage Tool for Emergency Department Care, Version 4. Implementation Handbook 2012 Edition. AHRQ. ISBN 978-1-58763-416-1.