A Practical Guide to Trauma Scoring Systems for Trauma Registry Professionals

Trauma program leaders use trauma scores to monitor and improve quality of care. Three of the most important trauma scoring systems are the Injury Severity Score (ISS), the New Injury Severity Score (NISS) and the Trauma Injury Severity Score (TRISS).

ISS and NISS are very similar, and TRISS is based in part on ISS. All three scores play an important role in trauma performance improvement (PI). However, there are key differences in how these scores are calculated and how they are used in trauma program management.

Most registry software systems automatically calculate the ISS, NISS and TRISS for all trauma patients. However, trauma registry professionals who understand the underlying formulas will do a better job of managing data quality.

Q. How do you calculate the ISS?

After you have assigned Abbreviated Injury Scale (AIS) codes to a patient’s injuries, identify the three most severely injured ISS body regions. Take the highest AIS severity code in each of these three regions, square each AIS code and then add the three squared numbers.

For example, a patient has a head injury with an AIS severity code of 4, a face injury with an AIS severity code of 1, a chest injury with an AIS severity code of 3, and an abdominal injury with an AIS severity code of 2. The three most severely injured body regions are head (4), chest (3) and abdomen (2). The ISS calculation is:

4² + 3² + 2² = ISS

16 + 9 + 4 = 29

ISS values range from 1 to 75. If any injury is assigned an AIS of 6 (maximal injury), the ISS is automatically the maximum score of 75.

Remember that the ISS body regions are:

• Head or neck (includes cervical spine)
• Face
• Chest (includes thoracic spine)
• Abdominal or pelvic contents (includes lumbar spine)
• Extremities or pelvic girdle
• External

Q. How do you calculate the NISS?

The New Injury Severity Score (NISS) is similar to the ISS, except it is calculated using the patient’s three most severe injuries regardless of the body region in which they occur.

For example, a patient with multiple gunshot wounds to the abdomen sustains injuries to their small intestine, liver and kidney, with AIS severity codes of 3, 4 and 5, respectively. Since these three injuries are all to one body region (the abdomen), the ISS calculation would only include the kidney injury. However, the NISS calculation will include all three abdominal injuries.

To calculate the NISS, square each AIS severity code and then add the three squared numbers. In the GSW patient example above, the calculation would be:

3² + 4² + 5² = NISS

9 + 16 + 25 = 50

Q. How do you calculate the TRISS?

The components of the Trauma Injury Severity Score (TRISS) are the patient’s ISS, the patient’s Revised Trauma Score (RTS) and the patient’s age. The components of RTS are Glasgow Coma Scale (points), systolic blood pressure (mmHg) and respiratory rate (breaths per minute).

The TRISS equation is a complex logarithmic regression. As noted above, most registry software systems automatically calculate the TRISS. You can also use an online TRISS calculator to score patients manually.

The main takeaway is that TRISS takes into account both physiologic parameters and information about the patient’s injury to predict probability of survival.

Q. How are ISS, NISS and TRISS used in trauma care?

Since the ISS is based on the patient’s three most severely injured body regions, it is most useful for patients with multiple injuries across multiple body systems — for example, a crash or fall victim with several neurologic and orthopedic injures.

Since the NISS is based on the patient’s three most severe injuries regardless of the body region in which they occur, it is most useful for patients whose injuries are concentrated in one system — for example, a patient with a GSW to the abdomen (as in the above example) or a patient with multiple injuries to the chest. In general, the NISS is an important tool for trauma centers that see a high volume of patients with penetrating injuries or multiple injuries concentrated to one body region.

Since the TRISS determines a patient’s probability of survival (PS), it is useful for evaluating care by comparing actual outcomes to predicted outcomes. (Note: Because TRISS incorporates ISS, it is more useful when evaluating patients with multisystem trauma and less useful when evaluating patients with injuries concentrated in one system.)

All three scores play an important role in a trauma PI program. For example:

Data validation. ISS values help trauma program leaders and trauma registrars monitor data quality. For example, any record with an ISS of 75 (maximal injury) or no ISS should be checked for accuracy.

Primary review. ISS scores help trauma PI coordinators identify cases requiring further review. For example, any patient with an ISS greater than 9 who was admitted to a nonsurgical service should be reviewed since this represents potential undertriage.

Secondary and tertiary review. Every trauma case presentation should include the patient’s ISS and TRISS. These scores give the trauma medical director or the peer panel a starting point for assessing the condition of the trauma patient and the anticipated outcome. If the patient had a cluster of injuries in one body region, the case presentation should also include the NISS. (For more information on the PI review process, read Manage levels of review more efficiently with event review templates.)

TQIP benchmark report review. When a trauma center has an outlier value on its TQIP benchmark reports, trauma program staff can use the drill-down feature to analyze the specific patient cohort for commonalities. For example, a TQIP report shows that a center is an outlier on “days to withdrawal of care.” The drill-down shows that the common factors are ISS greater than 17 and one or more organs failing. For future trauma patients, these factors could be considered a trigger to consult palliative care.

Q. How do injury grading systems contribute to trauma scores?

The AIS Dictionary has incorporated several specialized injury grading systems that enable registrars to assign more accurate severity codes for certain injuries. Greater accuracy in coding contributes to more accurate ISS, NISS and TRISS scores for these injuries.

The ASIA Impairment Scale (or “ASIA Grade”) from the American Spinal Injury Association is a standard neurological classification of spinal cord injury that has clear and unambiguous definitions for grading the degree of spinal impairment. The ASIA Grades are A through E, with “A” being a complete injury (no motor or sensory function preserved) and “E” being normal motor and sensory function.

The Duma Eye Score (DES) is a 4 -point eye injury severity scale that takes into account the need for ocular surgery, expected recovery time and possible loss of sight. The scale range is 1 through 4, with “1” being minor eye injury and “4” being severe injury resulting in blindness.

The Organ Injury Scale (OIS) is a classification scheme based on the anatomic disruption of an individual organ, scaled from 1 (least severe) to 6 (most severe). The OIS actually encompasses three different scales, covering spleen/liver/kidney injuries, renal trauma and pancreatic trauma. For complete details on these scaling systems, visit the AAST’s Organ Injury Scale page.

Injury severity in OIS is based solely on threat to life (in comparison, the AIS encompasses other dimensions of injury severity). Total integration of AIS and OIS has not been possible because some OIS descriptors are too detailed for the AIS at this stage in its evolution.

• When assigning AIS codes, the clinical description of the injury within the documentation takes precedence over the OIS grade.
• However, if the only available documentation is the OIS grade, it can be used when assigning an AIS code.

The Knight and North (KN) Classification describes zygoma (cheekbone) fractures. The scale range is I to VI, with “I” being no significant displacement and “VI” being complex fractures.

Q. Does AIS incorporate any other injury grading systems?

Several other scoring systems have been developed to grade injuries to different body systems.

• For example, the DAI grading system classifies diffuse axonal injuries into three categories based upon histological findings in the anatomical distribution of injury.
• In addition, the new CBI-M framework classifies traumatic brain injury based on four pillars: clinical, biomarker, imaging and modifiers.

While these and other trauma scoring systems are currently being used by trauma providers, they are not currently used within the AIS coding. However, these scoring systems are being considered by the AIS Content Committee for future revisions of the AIS Dictionary.

Q. How can we improve the accuracy of our trauma scores?

All three of these trauma scores (ISS, NISS and TRISS) depend on AIS codes. Therefore the best way to improve trauma score accuracy is for trauma registrars to develop their AIS coding skills. Some effective strategies are:

Keep up with data validation. A strong data validation process will help registrars continuously improve their AIS coding skills. Registrars can use logic validation registry reports to identify field values that indicate a potential AIS coding mistake.

For example, a logic validation report might flag charts that include an ICU days value but an ISS less than 9 — a situation that is possible, but not likely. Reviewing these charts is an opportunity to check the AIS coding and help registrars learn from any mistakes.

It is also important to keep up with inter-rater reliability (IRR) checks. An important step in the IRR process is validating the patient’s injuries and verifying that chosen AIS codes reflect all available injury detail. At a minimum, an IRR check should look at the diagnosis; specific details about that diagnosis such as the location, size, complexity, etc.; and the AIS code assigned. The check process should also include the manual recalculation of the ISS.

Code difficult cases as a team. Any time a registrar is having difficulty assigning an AIS code, he or she should feel empowered to call upon other members of the registry team for assistance.

Even the most experienced registrar or data manager will sometimes need another set of eyes on a chart and another interpretation on how to code a case. Any learning points gleaned from these interactions should be shared with the entire registry team. If it’s a problem for you, it will be a problem for someone else in the future.

If you are a one-person department and you encounter a difficult case to code, reach out to fellow trauma professionals within your network for opinions.

Leverage AAAM resources. Many coding resources are available on the Association for the Advancement of Automotive Medicine (AAAM) website, including AIS webinars, courses and publications.

The newest AAAM resource is AIS Digital, which is the official digital version of the AIS Dictionary. The multi-platform AIS Digital app can calculate various trauma scores (including ISS and NISS) and it includes a three-dimensional avatar that can map injury patterns across individual patients.

Registry professionals can also contact the AAAM directly with any coding questions — email Kathy Cookman at kcookman@aaam.org.

Commit to professional development. Trauma center standards from the American College of Surgeons (ACS) include several requirements covering continuing education for trauma registry professionals.

Standard 4.33 of Resources for Optimal Care of the Injured Patient: 2022 Standards (July 2025 Revision) requires registry staff to participate in an AIS training course, a trauma registry course and an ICD-10 course. (For full details, see How the trauma registry team must be educated.)

In addition, Standard 4.32 states that at least one member of the trauma registry team must be a current Certified Abbreviated Injury Scale Specialist (CAISS). (To learn more, see How the trauma registry team must be staffed.)