injury severity score injury severity score the injury severity score (iss) is an established medical score to assess trauma severity. it correlates with mortality, morbidity and hospitalization time after trauma. it is used to define the term major trauma. a major trauma (or polytrauma) is defined as the injury severity score being greater than 15. the ais committee of the association for the advancement of automotive medicine (aaam) designed and improves upon the scale. injury severity score abbreviated injury scale (ais) the abbreviated injury scale (ais) is an anatomically based consensus-derived global severity scoring system that classifies each injury in every body region according to its relative severity on a six-point ordinal scale: minor moderate serious severe critical maximal (currently untreatable). there are nine ais chapters corresponding to nine body regions: head face neck thorax abdomen spine upper extremity lower extremity external and other. definition the iss is based (see below) upon the abbreviated injury scale (ais). to calculate an iss for an injured person, the body is divided into six iss body regions. these body regions are: head or neck – including cervical spine face – including the facial skeleton, nose, mouth, eyes and ears chest – thoracic spine and diaphragm abdomen or pelvic contents – abdominal organs and lumbar spine extremities or pelvic girdle – pelvic skeleton external to calculate an iss, take the highest ais severity code in each of the three most severely injured iss body regions, square each ais code and add the three squared numbers for an iss (iss = a2 + b2 + c2 where a, b, c are the ais scores of the three most injured iss body regions). the iss scores ranges from 1 to 75 (i.e. ais scores of 5 for each category). if any of the three scores is a 6, the score is automatically set at 75. since a score of 6 ("unsurvivable") indicates the futility of further medical care in preserving life, this may mean a cessation of further care in triage for a patient with a score of 6 in any category.