It is important to recognize that ICD diagnosis codes and AIS severity codes were developed for two very different purposes.  ICD diagnosis codes were developed to classify and code diagnoses and symptoms.

AIS is a scoring system used to identify the severity of a single injury based on anatomical derangement.   AIS codes are generally much more specific than ICD diagnosis codes, therefore mapping from ICD to AIS is improved when the most specific ICD diagnosis code is used.  Medical records ICD coding is used for reimbursement purposes.  Within trauma centers, the ICD diagnosis codes entered into the trauma registry are often more specific in identifying the individual injury than the diagnosis codes supplied by medical records.  The most specific ICD diagnosis codes promote the best translation in the AAAM ICD to AIS maps.