Injury Severity Score Calculator

The Injury Severity Score converts a list of anatomical injuries into one number that predicts survival. Each injury is first coded on the Abbreviated Injury Scale from 1 (minor) to 6 (currently untreatable), then the worst AIS in each of six body regions - head and neck, face, chest, abdomen and pelvic contents, extremities and pelvic girdle, and external or skin - is identified. The three highest of those six are squared and summed, giving a range of 0 to 75. The squaring is the point of the method: mortality does not rise linearly with injury severity, so an AIS 5 contributes 25 while an AIS 2 contributes only 4, which reproduces the steep, convex relationship between anatomical damage and death that Baker observed in autopsy and registry data. Any single AIS of 6 forces the score to 75 by convention. Practitioners generally treat ISS above 15 as major trauma, the usual threshold for trauma registry inclusion, trauma team activation review, and trauma center benchmarking; ISS above 25 marks a group with substantially higher mortality and ICU demand. The main limitations are that ISS ignores physiology, age, and comorbidity, counts only one injury per region so that two critical chest injuries score no worse than one, and is entirely dependent on the accuracy of AIS coding by trained registrars. It also treats an AIS 3 head injury and an AIS 3 limb injury as equivalent even though their prognoses differ sharply.

The ISS was introduced in 1974 by Susan P. Baker, Brian O'Neill, William Haddon Jr., and William B. Long in the Journal of Trauma, in a paper analyzing motor vehicle crash fatalities. Baker, an epidemiologist at Johns Hopkins, was looking for a way to compare patients with multiple injuries when existing single-injury descriptions could not express cumulative burden. Their key empirical finding was that the sum of squares of the three worst regional AIS values tracked mortality far better than the simple sum, which is why the squaring step survives unchanged more than fifty years later. The scale it rests on, the Abbreviated Injury Scale, was first published in 1971 by a joint committee of the American Medical Association, the Society of Automotive Engineers, and the Association for the Advancement of Automotive Medicine, originally to standardize crash injury reporting. The AAAM has revised it repeatedly - notable dictionary updates appeared in 1985, 1990, 1998, 2005, and 2015 - and each revision shifts some ISS values, which complicates comparison of registry data across eras. In 1997 Turner Osler, Susan Baker, and William Long proposed the New Injury Severity Score, which squares the three worst injuries regardless of region and predicts outcome better in penetrating trauma and in patients with several severe injuries in one region. Despite that, the original ISS remains the standard descriptor in trauma registries and in the TRISS methodology developed by Boyd and colleagues in 1987.