ISS Calculator
Calculate ISS, NISS, and TRISS probability of survival from AIS body region severity scores
Select the worst AIS severity score for each body region. Leave at 0 (None) if the region was not injured.
Brain, skull, cervical spine, spinal cord at cervical level
Facial skeleton, nose, mouth, eyes, ears
Chest wall, rib cage, thoracic spine, diaphragm, lungs, heart, great vessels
Abdominal organs (liver, spleen, kidneys, bowel), pelvic contents, lumbar spine
Arms, legs, pelvic girdle, sprains, fractures, dislocations, vascular injuries
Skin: lacerations, contusions, burns, hypothermia, near-drowning, crush
Enter AIS Body Region Scores
Select the worst AIS severity for each injured body region above. ISS, NISS, and severity classification will appear here.
How to Use the ISS Calculator
Assess and Score Each Body Region
For each of the six ISS body regions (Head/Neck, Face, Thorax, Abdomen, Extremities, External), select the AIS severity code that best describes the worst injury in that region. Use 0 (None) for uninjured regions. AIS codes range from 1 (Minor) through 5 (Critical) to 6 (Unsurvivable). Score based on complete injury diagnosis, not initial presentation alone.
Review Your ISS and Severity Classification
The calculator automatically computes ISS as the sum of the squares of the top three AIS scores from different regions. If any region scores AIS-6, ISS is automatically set to 75. Review the severity classification (Minor: 1-8, Moderate: 9-15, Severe: 16-24, Very Severe: 25-74, Maximal: 75) and note the major trauma flag if ISS exceeds 15.
Compare ISS with NISS
Review the NISS (New Injury Severity Score), which counts the three highest AIS scores regardless of body region. If NISS equals ISS, the three most severe injuries are in different regions. If NISS is greater than ISS, the patient has multiple serious injuries in the same body region, which ISS underweights. NISS is typically preferred for penetrating trauma patients.
Calculate TRISS Survival Probability (Optional)
Expand the TRISS Calculator section and enter the patient's Glasgow Coma Scale score (3-15), systolic blood pressure (mmHg), respiratory rate (breaths/min), age, and injury mechanism (blunt or penetrating). The calculator will compute the Revised Trauma Score (RTS) and TRISS probability of survival — a population-level estimate useful for trauma audit and quality improvement.
Frequently Asked Questions
What is the Injury Severity Score (ISS) and who uses it?
The Injury Severity Score (ISS) is a validated anatomic scoring system that quantifies overall trauma severity in patients with multiple injuries. It was developed by Baker et al. in 1974, initially validated on motor vehicle collision patients in Baltimore. ISS is used worldwide by trauma surgeons, emergency physicians, trauma registrars, and researchers. It is required for designation by the American College of Surgeons Committee on Trauma and is used in trauma registries such as NTDB, TQIP, and ACS TQIP. Primary applications include trauma quality improvement, benchmarking between trauma centers, research publications, resource allocation, and regulatory reporting. ISS is not appropriate for acute bedside triage, as complete injury diagnosis is required before scoring.
Why does ISS = 75 automatically when any region scores AIS-6?
An AIS-6 injury is by definition unsurvivable — it represents injuries that are incompatible with life based on the AIS coding system. Examples include decapitation, complete crush injury to the head, traumatic hemipelvectomy, or massive burns exceeding 90% body surface area. When any body region is assigned AIS-6, no mathematical calculation is needed because the injury itself is defined as non-survivable. Setting ISS automatically to 75 prevents misleading scores — without this rule, a patient with AIS-6 head and AIS-1 facial injuries would score only 36 + 1 = 37, which fails to reflect the gravity of the situation. The automatic maximum of 75 is also mathematically the highest achievable score (5² + 5² + 5² = 75).
What is the difference between ISS and NISS, and when does it matter?
ISS (Injury Severity Score) uses only the highest AIS score from each of the six body regions, then squares and sums the top three regional scores. This means if a patient has two chest injuries rated AIS-4 and AIS-3, ISS only counts the AIS-4 for the thorax region. NISS (New Injury Severity Score) removes this restriction and uses the three highest AIS scores from any body regions. In our chest injury example, NISS would count both AIS-4 and AIS-3 thorax injuries, giving a higher and arguably more accurate score. Research has shown NISS outperforms ISS for predicting mortality and complications in penetrating trauma patients and those with concentrated single-region injuries. For classic multisystem blunt trauma affecting different regions, ISS and NISS often agree. In the absence of multiple same-region injuries, NISS always equals ISS.
What does TRISS probability of survival mean clinically?
TRISS (Trauma Injury Severity Score) is a logistic regression model that generates a probability of survival (Ps) from 0 to 100 percent for a given patient profile. The Ps is calculated using ISS (anatomic severity), RTS (physiologic status: GCS + SBP + RR), age group, and injury mechanism. A Ps of 0.85 means that based on historical MTOS database outcomes, 85% of patients with this profile would be expected to survive. TRISS is not a prognosis for the individual patient — it is a population-level benchmark. Its primary use is in trauma quality improvement: if a patient with a Ps of 0.90 dies, clinicians investigate whether care factors contributed. If a patient with Ps of 0.10 survives, this is documented as an unexpected survivor, highlighting potentially exceptional care or underestimated resilience.
What is the Revised Trauma Score (RTS) and how is it calculated?
The Revised Trauma Score (RTS) is a physiologic scoring system that quantifies hemodynamic and neurological status using three parameters: Glasgow Coma Scale (GCS), systolic blood pressure (SBP), and respiratory rate (RR). Each parameter is coded to a value of 0-4 based on specific ranges. GCS 13-15 = 4, GCS 9-12 = 3, GCS 6-8 = 2, GCS 4-5 = 1, GCS 3 = 0. SBP greater than 89 = 4, SBP 76-89 = 3, SBP 50-75 = 2, SBP 1-49 = 1, SBP 0 = 0. RR 10-29 = 4, RR over 29 = 3, RR 6-9 = 2, RR 1-5 = 1, RR 0 = 0. These coded values are weighted and summed: RTS = (0.9368 × GCS_coded) + (0.7326 × SBP_coded) + (0.2908 × RR_coded), giving a range of 0 to 7.84. An RTS below 4 suggests the patient should be transferred to a designated trauma center.
How accurate is ISS, and what are its main limitations?
ISS has been validated across hundreds of thousands of trauma patients and reliably predicts mortality, hospital length of stay, ICU admission rates, and resource utilization at the population level. Its primary limitations are well established. First, only the highest AIS per body region is counted, causing ISS to underestimate severity when multiple serious injuries occur in the same region — NISS addresses this. Second, ISS requires complete injury assessment including imaging, operative findings, and final diagnoses, so it cannot be calculated during the acute resuscitation phase. Third, the scoring is entirely anatomic with no physiologic data — a patient with identical ISS scores can have vastly different outcomes based on physiologic reserve, age, comorbidities, and time to care. Fourth, accurate AIS coding is complex and requires dedicated training, meaning inter-rater reliability can vary. Fifth, ISS was developed and validated in adult trauma populations and is less well-calibrated for pediatric injuries.