Prior to 2003, external causes of injury codes "E codes" are included in the diagnosis array (DXn). Beginning in 2003, any separately reported E codes and any E codes encountered in the diagnosis array are placed in a separate array specific to E codes (ECODEn).

E codes reported on a discharge record are compared to a list of valid E codes 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). A year window (six months before and six months after) is allowed. Invalid E codes are masked directly and Clinical Classifications Software (CCS) data elements (E_CCSn) are set to invalid (.A).

The maximum number of E codes reported varies by state. HCUP retains all E codes provided by the data source in the State Inpatient Databases, but only the first four E codes are retained on the NIS.

California does not require the reporting of E-codes in the range E870-E879 (misadventures and abnormal reactions).

South Carolina does not provide to HCUP E-codes in the range E870-E879 (misadventures and abnormal reactions).

Washington does not require hospitals to report E-codes in the range E870-E879 (misadventures and abnormal reactions) to the state data organization.