ISS — Injury Severity Score
Anatomical scoring system for trauma severity based on AIS regions.
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Why use it
Standard research and trauma registry metric. ISS ≥16 defines major trauma. Predicts mortality, hospital LOS, and resource utilization.
About
The Injury Severity Score (ISS) is an anatomical scoring system for trauma patients. It uses the Abbreviated Injury Scale (AIS) to score injuries in 6 body regions, then sums the squares of the three most severely injured regions.
When to use
- Trauma patients with injuries in multiple body regions
- Trauma registry and epidemiological research
- Benchmarking trauma center performance
- Triage and resource allocation decisions
Formula
Pearls & pitfalls
- Only the highest AIS in each body region counts.
- ISS = sum of squares of the 3 highest AIS region scores.
- AIS = 6 in any region automatically sets ISS = 75.
- ISS does not account for multiple injuries in the same body region.
- New Injury Severity Score (NISS) = sum of squares of 3 highest AIS regardless of region (may be superior).
Next steps
ISS <9: Minor trauma. ISS 9-15: Moderate. ISS 16-24: Severe. ISS ≥25: Critical. ISS = 75 if any AIS = 6 (unsurvivable). Consider TRISS for mortality prediction combining ISS with RTS and age.
Evidence
Baker et al. J Trauma 1974. Validated against mortality in thousands of trauma patients. ISS ≥16 = major trauma threshold widely adopted.