In the HCUP databases, ICD-9-CM external cause of injury codes (E codes) are represented as 4- to 5-character alphanumeric codes with implicit decimals (i.e., decimals not included). Prior to data year 2014, the HCUP data elements for E Codes are length 5; in 2014, they are length 7. The first digit is the character E with all subsequent digits being numeric. The codes are left-justified in the HCUP databases so that prior to 2014 there is one space following a 4-character E code (three spaces in 2014). For example, the E code E916 would appear as 'E916 ' with a trailing blank in HCUP data and the code E917.1 would appear as 'E9171'.

The storage of E codes in the HCUP databases varies by data year:

• Beginning in October 2015, International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) external cause of morbidity codes are stored in the data element I10_ECAUSEn.
• From January 2003 through September 2015, any separately reported E codes and any ICD-9-CM E codes encountered in the diagnosis array are placed in a separate array specific to E codes (ECODEn).
• Prior to 2003, ICD-9-CM E codes are included in the diagnosis array (DXn).

E codes are compared to a list of ICD-9-CM codes valid for the discharge date. Anticipation of or lags in response to official ICD-9-CM coding changes are permitted for discharges occurring within a window of time around the official ICD-9-CM coding changes (usually October 1). In the data prior to 1998, a six months window (three months before and three months after) is allowed. Beginning in the 1998 data, a year window (six months before and six months after) is allowed. Invalid and inconsistent E codes are masked directly. Clinical Classifications Software (CCS) data elements are coded with respect to the E code.

Beginning in data year 2009, hospitals in Arizona are required to report E codes for an injury diagnosis in the range 800-999. In addition, the number of E codes that could be retained on a discharge record increased.

Prior to data year 2010, California did not require the reporting of E-codes in the range E870-E879 (misadventures and abnormal reactions).

Starting in 2003, the Georgia Hospital Association requires that any ICD-9-CM diagnosis codes indicating medical misadventures (E870-E879) and adverse reactions (E940-E949) be excluded from the list of diagnosis codes on the record.

South Carolina does not provide to HCUP E-codes in the range E870-E876 (misadventures and abnormal reactions).