Injury Severity Score

The Injury Severity Score (ISS) assesses the combined effects of the multiply-injured patients and is based on an anatomical injury severity classification, the Abbreviated Injury Scale (AIS). The ISS is an internationally recognised scoring system which correlates with mortality, morbidity and other measures of severity.

The ISS is calculated as the sum of the squares of the highest AIS code in each of the three most severely injured ISS body regions. These body regions are:

  • Head or neck
  • Face
  • Chest
  • Abdominal or pelvic contents
  • Extremities or pelvic girdle
  • External
Injury Severity Scores range from 1 to 75. If an injury is assigned an AIS of 6 (identifying a currently untreatable injury), the ISS score is automatically assigned 75.

ISS body regions

There are only 6 Injury Severity Score (ISS) Body Regions to which injuries can be assigned, although the AIS 2005 - Update 2008 dictionary is divided into 9 anatomical chapters.

The following may assist with assigning the body regions.

Head or neck injuries include injury to the brain or cervical spine, skull or cervical spine fractures and asphyxia/suffocation.

Facial injuries include those involving mouth, ears, nose and facial bones.

Chest injuries include all lesions to internal organs, drowning and inhalation injury. Chest injuries also include those to the diaphragm, rib cage, and thoracic spine.

Abdominal or pelvic contents injuries include all lesions to internal organs. Lumbar spine lesions are included in the abdominal or pelvic region.

Extremities or pelvic girdle injuries include sprains, fractures, dislocations and amputations.

External and other trauma injuries include lacerations, contusions, abrasions, and burns, independent of their location on the body surface, except amputation burns that are assigned to the appropriate body region. Other traumatic events assigned to this ISS body region are: electrical injury, frostbite, hypothermia and whole body (explosion-type) injury.

ISS scoring rules

The ISS is the sum of the squares of the highest AIS code in each of the three most severely injured ISS Body Regions.

The following example demonstrates an ISS calculation:

ISS Body Region* Injury AIS Code Highest AIS AIS²
HEAD/NECK Cerebral contusion NFS
Internal carotid artery transection (neck)
140602.3
320212.4
4 16
FACE Closed fractured nose 251000.1 1  
CHEST Rib fractures left side, ribs 3 – 4 450202.2 2  
ABDOMEN Retroperitoneal Haematoma 543800.2 2 4
EXTREMITIES Fractured femur (NFS) 853000.3 3 9
EXTERNAL Abrasions (NFS) 910200.1 1  
    ISS = 29
* Note that these ISS Body Regions do not necessarily coincide with the chapters used in the AIS 2005 - Update 2008 dictionary.

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