Triage is a system for sorting patients by how urgently they need medical care. When more people need help than can be treated at once, triage determines who goes first. The word comes from the French “trier,” meaning to sort, and the concept dates back to 1792 when Baron Dominique Jean Larrey, Napoleon’s chief surgeon, developed the first systematic approach to prioritizing wounded soldiers on the battlefield. Today, triage happens every day in emergency departments, on battlefields, and at disaster scenes around the world.
How Emergency Department Triage Works
When you walk into an emergency room, you don’t see a doctor right away. A triage nurse evaluates you first, typically within 10 to 15 minutes of arrival. The nurse checks your vital signs, asks about your symptoms, and assigns you a priority level that determines how quickly you’ll be seen. This isn’t a first-come, first-served system. Someone who arrived after you with a more serious condition will be taken back before you.
Most U.S. emergency departments use the Emergency Severity Index, or ESI, a five-level system that works like a decision tree. The first question the nurse considers is blunt: “Is this patient dying?” They check whether you have a clear airway, whether you’re breathing, and whether you have a pulse. If you need immediate life-saving intervention, you’re classified as ESI Level 1 and taken straight to a treatment area.
If you’re not in that critical category, the nurse asks a second set of questions. Are you in a high-risk situation? Are you confused, lethargic, or disoriented? Are you in severe pain or distress? If the answer to any of these is yes, you’re assigned Level 2 and treated as an emergency. For everyone else, the nurse estimates how many hospital resources you’ll need (lab tests, imaging, IV fluids, specialist consults) and assigns Level 3 (urgent), Level 4 (nonurgent), or Level 5 (minor). A broken ankle that needs an X-ray and pain management lands differently than a sore throat that just needs a quick exam.
This judgment call relies heavily on nursing experience. Two patients can walk in with the same complaint and receive different levels based on subtle differences in how they look, their vital signs, and their medical history.
What the Priority Levels Mean for Wait Times
Your triage level directly controls how long you wait. In Europe, the widely used Manchester Triage System ties each category to a maximum wait time: immediate cases have a target of zero minutes, very urgent cases should be seen within 10 minutes, urgent within 60 minutes, standard within 120 minutes, and non-urgent within 240 minutes. U.S. hospitals don’t use identical benchmarks, but the principle is the same. A Level 1 patient is never waiting. A Level 5 patient could be in the waiting room for hours.
This is why you can sit in an ER for a long time even when you arrived early. It’s not disorganization. It means the people being seen ahead of you are sicker than you are, which is actually a good sign about your own condition.
Vital Signs That Trigger the Highest Priority
Certain measurements automatically push a patient to the most urgent category. A systolic blood pressure below 80, a heart rate below 40 or above 140 beats per minute, a body temperature below 95°F or above 105.8°F, or a severely depressed level of consciousness all flag a patient as Level 1. Oxygen saturation below 90%, unresponsiveness, absence of a pulse, or severe respiratory distress also qualify. These thresholds exist because patients hitting those numbers have a high likelihood of rapid deterioration.
Disaster Triage and Color-Coded Tags
Emergency department triage sorts patients into numbered levels. Disaster triage uses a different approach because the scale of the problem is fundamentally different. In a mass casualty event like an earthquake, bombing, or chemical spill, responders may face dozens or hundreds of patients at once with limited supplies and personnel. The goal shifts from giving everyone the best possible care to saving the greatest number of lives.
The most common disaster triage system in the U.S. is called START (Simple Triage and Rapid Treatment). It uses four color-coded tags:
- Red (Immediate): Life-threatening injuries that require urgent intervention but are survivable with treatment. These patients are transported first.
- Yellow (Delayed): Serious injuries, but the patient’s condition is not expected to deteriorate significantly over several hours. Transport can wait.
- Green (Minor): Relatively minor injuries unlikely to worsen over days. These are the “walking wounded” who may even be able to help care for themselves or others.
- Black (Expectant): Injuries so severe that survival is unlikely even with treatment, or the patient is already dead. In a resource-scarce situation, these patients receive comfort care rather than aggressive intervention.
A START assessment takes about 30 seconds per patient. Responders check four things in order: Can the person walk? Are they breathing, and if so, is their breathing rate above or below 30 breaths per minute? Do they have a palpable pulse at the wrist? Can they follow simple commands? Each answer routes the patient along a decision tree to one of the four color categories.
How Triage Differs for Children
Children aren’t small adults, and their triage requires adjusted criteria. The most widely used pediatric disaster triage system is JumpSTART, a modified version of START designed for patients roughly 1 to 8 years old. Normal respiratory rates are higher in young children, so the thresholds shift accordingly. A breathing rate that would be alarming in an adult might be perfectly normal in a toddler.
JumpSTART also adds a step that START doesn’t include. If a child isn’t breathing, the responder attempts to open the airway before assigning a black tag. Children are more likely than adults to stop breathing due to a simple airway obstruction rather than a fatal injury, so that brief intervention can change the outcome.
The Ethics of Triage Under Scarcity
Triage becomes an ethical challenge when resources run out entirely. During the COVID-19 pandemic, hospitals in some regions had to decide which patients would receive ventilators and which would not. These decisions fall under what’s called “crisis standards of care,” a framework with three core objectives: prevent harm, reduce health inequities, and show equal concern for every patient.
This is harder than it sounds. Early in the pandemic, many hospitals used organ failure scoring systems to rank patients for ventilator access. Subsequent research found that these scores alone worsened racial disparities in care. Incorporating age-aware approaches alongside clinical scores prevented more deaths and better reduced those inequities. The lesson was that triage systems built purely on physiological measurements can reflect and amplify existing health disparities if they aren’t designed with equity in mind.
AI in Triage Is Still Early
Hospitals are beginning to test whether artificial intelligence can assist with triage decisions. A 2025 study tested multiple AI models against physician triage assessments for over 39,000 emergency cases at a Greek university hospital. The best-performing models achieved only moderate agreement with experienced physicians on assigning ESI levels. For predicting whether a patient would need hospital admission, the top AI model correctly identified about 75% of patients who needed to be admitted and 76% of those who could be safely discharged.
Those numbers are promising but far from replacing human judgment. Some models showed a strong bias toward sending patients home, missing many who actually needed admission. Others leaned toward over-admitting, which would strain hospital capacity. For now, AI in triage remains a support tool rather than a decision-maker, and no system has come close to matching the nuanced clinical judgment of an experienced triage nurse.