Transition from ICD-9-CM to ICD-10-CM for Injury Emergency Department Visits and Hospitalizations

The International Classification of Diseases, Clinical Modification is used by health care organizations to code for injuries and illnesses. The coding system changed in October 2015 from the 9th revision (ICD-9-CM) to the 10th revision (ICD-10-CM). Since the ICD-10-CM codes provide much greater detail than ICD-9-CM, we do not recommend comparing clinical record data from October 2015 onward to data prior to October 2015 or reviewing trends that cross this transition.

Hospitalizations and emergency department visit queries for 2016 and later years use ICD-10-CM codes exclusively. Queries for 2015 and earlier years use ICD-9-CM codes. Fourth quarter data for 2015, when the transition to the new coding system occurred, are not included in either the ICD-9-CM or ICD-10-CM query. Because of this, the annual counts and rates for 2015 are estimates based on data from October 2014 through September 2015.

The major differences in the coding systems and the manner in which injury types are classified in these WISH modules are detailed below:

• Injury diagnoses codes expanded from 2,600 to about 43,000 codes.
• External cause of injury codes expanded from 1,300 to 7,500.
• Changes in the coding systems have impacted injury case definition and external cause and diagnosis groupings (in other words, how an injury is classified).
• ICD-9-CM codes do not distinguish between initial visits, follow-up visits, or treatment for sequelae. ICD-10-CM codes include information on the type of visit and we can therefore limit our dataset to initial visits for active treatment. This allows for rates and counts to more accurately reflect injury incidence, whereas ICD-9-CM could not.
• Injury types based on ICD-9-CM were classified using the first valid external cause of injury code only. If multiple causes of injury were listed in a record, only the first valid one was counted. The ICD-10-CM query module reviews all diagnosis and external cause of injury codes and classifies the injury based on any mention of an injury (for instance, a visit could be classified as a poisoning, if the code was found in a diagnosis field, AND a fall, if this was coded in an external cause of injury field).