The organization of care for patients arriving at a hospital emergency department (ED) depends on a rapid assessment process called triage. Triage is the method used to prioritize patients based on the severity of their condition, ensuring that the sickest individuals receive care first. In the United States and globally, the most commonly adopted and standardized system for this prioritization is the Emergency Severity Index (ESI). This system uses a five-level scale, with Level 1 indicating the greatest need for immediate intervention and Level 5 representing the least urgent need. The ESI algorithm helps emergency nurses quickly stratify patients by considering both the patient’s acuity, or stability, and the anticipated resources needed for their care.
Triage Levels 1 and 2: Resuscitation and Emergency
Patients assigned to Triage Level 1 are in need of immediate, life-saving interventions because their life, limb, or organ is under threat. This category, often called Resuscitation, is reserved for individuals who are clinically unstable and require treatment to begin within seconds. Examples include patients experiencing cardiac or respiratory arrest, those who are severely hypotensive and unresponsive, or individuals who must be intubated immediately to secure an airway. The ESI algorithm dictates that the triage nurse assigns Level 1 based on the need for this immediate, life-sustaining action alone.
Triage Level 2 patients are still considered high-acuity, but they do not require the instantaneous, life-saving interventions of Level 1. This category is assigned to patients who present with a high-risk situation, confusion, lethargy, severe pain, or signs that their condition could deteriorate rapidly. Conditions such as active chest pain suspicious for a heart attack, signs of stroke, or patients with new-onset, severe confusion often fall into Level 2. The key differentiator from Level 1 is that while the patient may be momentarily stable, they are time-sensitive, and a physician must evaluate them quickly, ideally within ten minutes.
Triage Level 3: Urgent Care and Required Resources
Patients who are clinically stable, not considered high-risk, and have reassuring vital signs are categorized as Triage Level 3. This is the first level where the anticipated consumption of hospital resources is used as a primary factor in determining the triage score. A patient is assigned Level 3 if the triage nurse predicts they will require “two or more resources” to reach a final diagnosis and disposition. Resources include diagnostic tools and treatments beyond a simple examination, such as laboratory blood work, complex X-rays, CT scans, or the administration of intravenous fluids or medications.
A patient presenting with moderate abdominal pain who will likely need both blood tests and a CT scan would be a Level 3 example. Similarly, a person experiencing a mild to moderate asthma exacerbation who requires both a chest X-ray and nebulized breathing treatments would meet the criteria for two resources. Because these patients are stable, they may experience a longer wait time than Levels 1 and 2. Their need for multiple complex resources distinguishes them from less acute categories. The resource-based assessment helps the ED manage internal flow by identifying patients who will occupy treatment space for longer periods due to the time required for testing.
Triage Levels 4 and 5: Non-Urgent and Minimal Needs
Triage Level 4 and Level 5 represent the lowest acuity categories, where patients are stable and have a low risk of deterioration. The difference between these two levels is based entirely on the number of anticipated resources needed for their care. A Level 4 patient is expected to require only “one resource” to complete their evaluation and treatment. This single resource might be a simple procedure like a laceration repair requiring sutures, an X-ray for an ankle sprain, or a single set of blood tests.
A Level 5 patient is the least urgent category, defined by the expectation that they will require zero resources beyond a physical examination and perhaps a simple prescription. Examples of Level 5 presentations include a patient seeking a prescription refill, a simple sore throat that may only require an oral medication, or a minor complaint that can be managed with simple wound care. These patients are considered non-urgent and can safely wait for extended periods, as their condition is not time-sensitive and requires minimal hospital services. The resource-based distinction helps hospitals identify patients who could potentially be treated more quickly in an urgent care setting or a dedicated “fast-track” area within the ED.