The Trauma Audit and Research Network

The Injury Severity Score (ISS)
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Those who are injured may have one or many injuries and the Injury Severity Score (ISS) is an anatomical score that measures the overall severity of injured patients.

All injuries are assigned an Abbreviated Injury Scale (AIS) code and score from an internationally recognised dictionary that describes over 2000 injuries and ranges from 1 (minor injury) to 6 (an injury that is thought to be ‘incompatible with life’). Patients with multiple injuries are scored by adding together the squares of the three highest AIS scores in three predetermined regions of the body. This is the ISS which can range from 1 to 75. Scores of 7 and 15 are unattainable because these figures cannot be obtained from summing squares. The maximum score is 75 (52+52+52). By convention, a patient with an AIS6 in one body region is given an ISS of 75. The injury severity score is non-linear and there is pronounced variation in the frequency of different scores; 9 and 16 are common, 14 and 22 unusual.

The assignment of AIS codes and scores are undertaken by trained coders within a Quality Assurance programme.

Case study
A man is injured in a fall at work. He complains of pain in his neck, jaw, and left wrist and has difficulty breathing. There are abrasions around the left shoulder, left side of the chest, and left knee.
Examination of the cervical spines (with radiography) suggests no abnormality. There is a displaced fracture of the body of the mandible. There are also fractures of the left wrist, and left ribs (4-9), with a flail segment.

Injury   AIS Score
Fracture of body of mandible   2

Fracture of lower end of radius
(not further specified*)

Fracture of ribs L 4-9 with flail segment   4
Abrasions (all sites)   1
Neck pain   0

AIS2005, Abbreviated injury scale

*If fracture of radius was known to be displaced or open the AIS would be 3. If not specified the lower score is used

Symptoms are not scored if there is no demonstrable anatomical injury

ISS = 22+22+42=24

For the purpose of the analysis described here, the ISS should be calculated only from operative findings, appropriate investigations, or necropsy reports. The overall injury severity score of a group of patients should be identified by the median value and the range, not the mean value. Non-parametric statistics should be used for analysis.