E codes are external causes of injury and poisoning codes.
The E code categories E000 and E800 - E999 are intended to provide the required information for injury research, and assessment of injury prevention strategies.
E code categories E001-E030 are activity codes that are used to report the activity of a patient requesting care for injuries and other health conditions, when the injury/health condition was the consequence of a certain activity or when the activity contributed to a condition.
E codes are important because they clearly indicate how the adverse effect, injury or poisoning occurred; whether it was inadvertent or accidental; or intentional such as assault or suicide; whether the patient seeking services is a civilian or military personnel; the related activity and the place where the event occurred.
E Code Categories Mainly Comprise

• Poisoning/adverse effects of drugs, medicinal substances and biological substances
• Transport accidents
• Accidents caused by fires/flames
• Accidental falls
• Accidents caused by environmental and natural factors
• Suicide or self inflicted injury
• Assaults or purposely inflicted injury
• Late effects of assaults, accidents or self injury

E codes are reported in outpatient clinics, hospitals, provider offices, emergency departments and other ambulatory centers.
General Coding Guidelines

• An E code belonging to the categories E800-E999 can be used with any code in the range 001-V91 that indicates an adverse effect due to an external cause, injury or poisoning.
  An activity E code falling in the range E001-E030 can be used with any code in the group 001-V91that indicates an injury/a health condition that developed due to an activity or the activity contributed to a condition.
  
• The full range of E codes E800 - E999 must be used to describe the cause, the place of occurrence and the intent with regard to all poisonings, injuries and adverse effects of drugs.
  
• For all initial encounters, assign the correct E code whether for injury, adverse effect of drugs or poisoning, not for ensuing treatments.
  E codes may however, be assigned while the acute fracture codes are still valid.
  
• Report as many E codes as necessary to explain each cause fully.
  
• An E code can never be used as a principal diagnosis.
  Understand that E codes are supplemental to ICD-9-CM diagnosis codes 001-V91.
  
• Never use an E code with a code from subcategory 995.
  9, except when the patient has another condition also (e.
  g.
  injury, poisoning, adverse effect of drugs) for which an E code is applicable.
  
• In case the reporting format limits the number of E codes that can be used, use the E code for the intent/cause that is most related to the principal diagnosis.
  If the format allows the use of additional E codes, the intent/cause of the additional events have to be reported instead of the codes for activity, external status or place.
  

Never Use an E Code as a First Listed or Principal Diagnosis on a Claim A CMS edit was established as of April 1, 2012 to reject electronic claims which had an E code as the principal or first listed diagnosis code.
Such a claim will not therefore be compliant with the HIPAA code set and transactions standards.
This directive is applicable to claims submitted on the CMS-1500 form as of January 1, 2013.
Medicare contractors have also been directed to return as unprocessable, claims reporting an ICD-9-CM E code as the principal diagnosis of Item 21 in the Form CMS-1500.
Adjustment and reprocessed claims that fail these edits will be denied.
This new CMS edit will be applicable to the equivalent ICD-10 CM diagnosis codes in the range V00-Y99 in the future.