15 things trauma physicians should know about AIS coding


Most physicians know very little about the Abbreviated Injury Scale (AIS), the scoring system used to calculate a patient’s Injury Severity Score (ISS). AIS codes are assigned by trauma registrars, a process that takes place largely “behind the scenes” at a busy trauma center.

However, simple mistakes or omissions in documentation can negatively impact AIS coding and lead to significant problems for trauma centers. Here is what happens:

  • Poor documentation of patient injuries leads to lower-than-appropriate AIS codes
  • Low AIS codes result in an ISS that does not reflect the true severity of a patient’s injuries
  • When an ISS is low, a patient death may be improperly classified as “unexpected mortality”
  • Higher than expected mortality rates lead to poor TQIP results
  • High mortality rates will also draw the attention of ACS surveyors and can lead to loss of trauma center designation

Inaccurate AIS coding can also undermine the value of the data in a trauma registry, undercutting the entire trauma team’s ability to conduct valid research.

Following are 15 facts about AIS coding that can help trauma physicians and other clinicians improve their documentation and generate better trauma data.

1. Lack of detail = low AIS code = low ISS

The key to documenting for AIS is to include as much relevant detail as possible. When documentation lacks specifics, it typically results in a not further specified (NFS) code, which usually generates a lower ISS.

For example, kidney injury without any further detail is assigned an AIS severity code of 2. Kidney laceration extending through the renal cortex, medulla and collecting system is assigned an AIS severity code of 4.

Note that for many injuries, measurement is critical. For example, a fracture is only considered displaced in AIS if it is more than 4 mm out of alignment. Say a patient has a nasal fracture that is displaced 5 mm. If you fail to document that, the injury will be coded as “nondisplaced” in AIS.

2. Clinical diagnosis of injury is generally not enough

In most cases, a clinical diagnosis alone is not sufficient to support an AIS code. In order to be coded in AIS, a diagnosis must be supported by documentation such as imaging studies or an autopsy report.

This is often an issue in documentation of fractures. A thorough physician note should state something like: “Fracture, right arm. Supporting evidence: Plain X-ray reading stating right distal radius fracture.”

Supporting documentation is critical for head injuries. An injury description of “closed head injury” or “traumatic brain injury” with no other supporting documentation will result in a “9” code, which cannot be used in calculating the patient’s ISS. In addition, cases with “9” codes are usually disqualified for inclusion in research.

There is one exception to this general principle: A concussion may be coded in AIS if the word “concussion” is written by the physician as the only brain injury diagnosis. However, this diagnosis supports a severity score of 1, indicating a minor injury.

3. Preliminary diagnoses are not codable in AIS

Only diagnoses can be coded in AIS. This means that “possible,” “suspected” or “rule out” diagnoses will not support an AIS code.

Improper use of electronic medical records is exacerbating this problem. Here is a common scenario: A radiologist enters “possible pneumothorax” or “suspected L-5 facet fracture” in the EMR. The trauma surgeon then copies that language from the EMR and pastes it into the physician note. Since the note documents a preliminary diagnosis, it cannot be used to generate an AIS code.

4. A mechanism of injury is not an injury

There are no AIS codes associated with mechanism of injury. Language such as “pedestrian struck by a car” or “burned in a house fire” does not generate an AIS code.

Make sure to specify the injury. This is often a matter of documenting any injury to the underlying structures or organs, not the external injury. For example, instead of “stabbed,” specify “transection of renal artery” or “4 cm laceration to spleen” as the case may be.

5. Complications are not injuries

Complications such as infection, DVT and epilepsy are not injuries and therefore are not codable in AIS. Complications are tracked in another screen of the trauma registry and are not a part of AIS coding.

6. Sequelae are generally not injuries

Conditions caused by or following an injury are generally not codable in AIS. Examples include death, blindness, swelling and miscarriage. In all of these events, be sure to document the primary injury — for instance, the eye injury that led to blindness.

However, there are a few exceptions to this principle: asphyxia, blood loss, air embolism, hemo/pneumothorax, brain edema/swelling and compartment syndrome. Note that in order to be coded in AIS, these conditions must meet the definition and rules listed in the Abbreviated Injury Scale Dictionary.

7. Iatrogenic injuries are not counted in AIS

AIS only considers injuries sustained in the traumatic event. For example, rib fractures sustained in a motor vehicle crash count toward the AIS code, but rib fractures sustained during CPR do not.

8. Death is not an injury

Many physicians and nurses assume that a patient mortality automatically yields an ISS of 75. This is not the case. Even if a patient dies, you still need to document each specific injury in order to facilitate appropriate AIS coding and an accurate ISS.

9. You cannot assume an injury occurred just because an outcome is present

For example, a hemothorax does not automatically mean lung laceration. Similarly, a blood transfusion does not automatically mean blood loss. Again, it is critical to substantiate and document the actual injuries that led to these outcomes.

10. Injuries that are not in the AIS Dictionary cannot be coded in AIS

There are some injury conditions that are not recognized as “stand alone” injuries in the AIS Dictionary. One example is hemoperitoneum. In the AIS system, blood in the peritoneal cavity must be associated with an abdominal injury and will be captured in that injury code.

11. Joints do not fracture

In the AIS system, joints may sprain or dislocate, but they do not fracture. When documenting a fracture, specify the fractured bone.

For example, in AIS there is no such thing as a “fractured hip.” Instead, specify either a fractured femur, a fractured acetabulum or both.

Another example: A “left ankle fracture” should instead be documented as a left fibula fracture, left tibia fracture, left talus fracture or some combination thereof.

12. Flail chest requires fractures in three or more adjacent ribs

Many physicians diagnose flail chest when two ribs are involved. In fact, the AIS definition of flail chest is three or more adjacent ribs each fractured in more than one location (for example, posterolateral and anterolateral) to create a free-floating segment. Note that under AIS, this condition may or may not result in paradoxical chest movement.

13. Loss of consciousness must be documented

In order for a registrar to code loss of consciousness (LOC), documentation must include convincing evidence of head injury and the diagnosis of LOC by a physician or physician extender. An EMS report of LOC may suffice if it is documented in the patient’s medical record by a physician, physician assistant or nurse practitioner.

14. When charting brain hematoma or hemorrhage, include perilesional edema

When documenting the size of a brain hematoma or brain hemorrhage, include any perilesional edema in the measurement. This will accurately describe the patient’s injury by including the whole area affected.

The AIS system recognizes that perilesional edema is an important element of injury severity. For instance, for an epidural cerebellum hematoma measuring 0.5 cm, the AIS severity is 2. For the same hematoma with 0.2 cm perilesional edema, the AIS severity is 4.

15. Diffuse axonal injury must meet specific requirements

In order for a registrar to code diffuse axonal injury (DAI) in AIS, the injury must meet the following requirements:

  • Immediate and prolonged coma (> 6 hours)
  • Radiographic proof of shearing lesions
  • No other reason for loss of consciousness
  • Physician must diagnose it

If any of these requirements are absent, the injury cannot be coded as DAI. For example, if MRI results state widespread axonal shearing injury but also show other mass lesions in the brain, the injury does not qualify as DAI under AIS.

Better documentation, better data

Trauma clinicians who master these concepts are well on their way to improving their documentation — and helping their registry team code their cases more accurately.

To take your documentation to the next level, learn more about AIS Training Courses. In addition, a new AIS coding course designed specifically for physicians will be available this fall.

Trauma Program Director, Kaiser Permanente Vacaville Medical Center
Chair of the Abbreviated Injury Scale Certification Board
Faculty for the Abbreviated Injury Scale Course

Kathy Cookman, BS, CSTR, CAISS, EMT-P, FMNP
CEO, KJ Trauma Consulting LLC
International Technical Coordinator/AIS Course Director, Association for the Advancement of Automotive Medicine

Recommended Resources

Association for the Advancement of Automotive Medicine. (2008). The Abbreviated Injury Scale Dictionary (2005- Update 2008 ed.). Barrington, IL: Association for the Advancement of Automotive Medicine.

Association for the Advancement of Automotive Medicine. (2008). Course Training Manual (The Abbreviated Injury Scale 2005-Update 2008). Barrington, IL: Association for the Advancement of Automotive Medicine.

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