Lit Matters 3: Emergency Severity Index Mis-Triage Rates

Emergency Severity Index triage misses matter most when low-acuity labels hide critical illness. ESI is widely used in US emergency departments, but large-scale data show mistriage is common, driven mostly by overtriage while a smaller undertriaged group carries the real safety signal.

Emergency Severity Index Mis-Triage

• Large cohort signal: A 5.3 million–encounter health system analysis found mistriage in 32.2% of ED visits, giving this paper unusual weight when thinking about how ESI performs in real practice.
• Undertriage safety problem: Undertriage was less common at 3.3%, but it is the clinically dangerous miss because patients labeled ESI III to V can deteriorate while still waiting for reassessment.
• Overtriage expected tradeoff: Overtriage accounted for 28.9% of encounters, reinforcing the core triage principle that false positives are often acceptable if the system reliably captures patients at risk of crashing.
• ESI III black box: Most undertriaged encounters were ESI III patients who likely belonged in ESI II, underscoring how the middle of the scale becomes a catch-all for uncertain acuity.
• Critical illness misses: Among patients who ultimately needed a level 1 intervention, 60.9% were undertriaged, a striking reminder that even the sickest patients are not always obvious at first pass. We get into why that number does and does not mean ESI is failing in the episode.
• Operational fix options: Nurse judgment remains central, but crowded departments with heavy boarding may benefit from physician-in-triage models when overtriage is overwhelming room placement and reassessment capacity.