The external causes of morbidity codes should never be sequenced as the first-listed or principal diagnosis.

External cause codes are intended to provide data for injury research and evaluation of injury prevention strategies. These codes capture how the injury or health condition happened (cause), the intent (unintentional or accidental; or intentional, such as suicide or assault), the place where the event occurred the activity of the patient at the time of the event, and the person's status (e.g., civilian, military).

There is no national requirement for mandatory ICD-10-CM external cause code reporting. Unless a provider is subject to a state-based external cause code reporting mandate or these codes are required by a particular payer, reporting of ICD-10-CM codes in Chapter 20, External Causes of Morbidity, is not required. In the absence of a mandatory reporting requirement, providers are encouraged to voluntarily report external cause codes, as they provide valuable data for injury research and evaluation of injury prevention strategies.

a. General External Cause Coding Guidelines

1) Used with any code in the range of A00.0-T88.9, Z00-Z99

An external cause code may be used with any code in the range of A00.0-T88.9, Z00-Z99, classification that is a health condition due to an external cause. Though they are most applicable to injuries, they are also valid for use with such things as infections or diseases due to an external source, and other health conditions, such as a heart attack that occurs during strenuous physical activity.

2) External cause code used for length of treatment

Assign the external cause code, with the appropriate 7th character (initial encounter, subsequent encounter or sequela) for each encounter for which the injury or condition is being treated.

Most categories in chapter 20 have a 7th character requirement for each applicable code. Most categories in this chapter have three 7th character values: A, initial encounter, D, subsequent encounter and S, sequela. While the patient may be seen by a new or different provider over the course of treatment for an injury or condition, assignment of the 7th character for external cause should match the 7th character of the code assigned for the associated injury or condition for the encounter.

3) Use the full range of external cause codes

Use the full range of external cause codes to completely describe the cause, the intent, the place of occurrence, and if applicable, the activity of the patient at the time of the event, and the patient's status, for all injuries, and other health conditions due to an external cause.

4) Assign as many external cause codes as necessary

Assign as many external cause codes as necessary to fully explain each cause. If only one external code can be recorded, assign the code most related to the principal diagnosis.

5) The selection of the appropriate external cause code

The selection of the appropriate external cause code is guided by the Alphabetic Index of External Causes and by Inclusion and Exclusion notes in the Tabular List.

6) External cause code can never be a principal diagnosis

An external cause code can never be a principal (first-listed) diagnosis.

7) Combination external cause codes

Certain of the external cause codes are combination codes that identify sequential events that result in an injury, such as a fall which results in striking against an object. The injury may be due to either event or both. The combination external cause code used should correspond to the sequence of events regardless of which caused the most serious injury.

8) No external cause code needed in certain circumstances

No external cause code from Chapter 20 is needed if the external cause and intent are included in a code from another chapter (e.g. T36.0X1- Poisoning by penicillins, accidental (unintentional)).

b. Place of Occurrence Guideline

Codes from category Y92, Place of occurrence of the external cause, are secondary codes for use after other external cause codes to identify the location of the patient at the time of injury or other condition.

Generally, a place of occurrence code is assigned only once, at the initial encounter for treatment. However, in the rare instance that a new injury occurs during hospitalization, an additional place of occurrence code may be assigned. No 7th characters are used for Y92.

Do not use place of occurrence code Y92.9 if the place is not stated or is not applicable.

c. Activity Code

Assign a code from category Y93, Activity code, to describe the activity of the patient at the time the injury or other health condition occurred.

An activity code is used only once, at the initial encounter for treatment. Only one code from Y93 should be recorded on a medical record.

The activity codes are not applicable to poisonings, adverse effects, misadventures or sequela.

Do not assign Y93.9, Unspecified activity, if the activity is not stated.

A code from category Y93 is appropriate for use with external cause and intent codes if identifying the activity provides additional information about the event.

d. Place of Occurrence, Activity, and Status Codes Used with other External Cause Code

When applicable, place of occurrence, activity, and external cause status codes are sequenced after the main external cause code(s). Regardless of the number of external cause codes assigned, generally there should be only one place of occurrence code, one activity code, and one external cause status code assigned to an encounter. However, in the rare instance that a new injury occurs during hospitalization, an additional place of occurrence code may be assigned.

e. If the Reporting Format Limits the Number of External Cause Codes

If the reporting format limits the number of external cause codes that can be used in reporting clinical data, report the code for the cause/intent most related to the principal diagnosis. If the format permits capture of additional external cause codes, the cause/intent, including medical misadventures, of the additional events should be reported rather than the codes for place, activity, or external status.

f. Multiple External Cause Coding Guidelines

More than one external cause code is required to fully describe the external cause of an illness or injury. The assignment of external cause codes should be sequenced in the following priority:

If two or more events cause separate injuries, an external cause code should be assigned for each cause. The first-listed external cause code will be selected in the following order:

External codes for child and adult abuse take priority over all other external cause codes.

See Section I.C.19., Child and Adult abuse guidelines.

External cause codes for terrorism events take priority over all other external cause codes except child and adult abuse.

External cause codes for cataclysmic events take priority over all other external cause codes except child and adult abuse and terrorism.

External cause codes for transport accidents take priority over all other external cause codes except cataclysmic events, child and adult abuse and terrorism.

Activity and external cause status codes are assigned following all causal (intent) external cause codes.

The first-listed external cause code should correspond to the cause of the most serious diagnosis due to an assault, accident, or self-harm, following the order of hierarchy listed above.

g. Child and Adult Abuse Guideline

Adult and child abuse, neglect and maltreatment are classified as assault. Any of the assault codes may be used to indicate the external cause of any injury resulting from the confirmed abuse.

For confirmed cases of abuse, neglect and maltreatment, when the perpetrator is known, a code from Y07, Perpetrator of maltreatment and neglect, should accompany any other assault codes.

See Section I.C.19. Adult and child abuse, neglect and other maltreatment

h. Unknown or Undetermined Intent Guideline

If the intent (accident, self-harm, assault) of the cause of an injury or other condition is unknown or unspecified, code the intent as accidental intent. All transport accident categories assume accidental intent.

1) Use of undetermined intent

External cause codes for events of undetermined intent are only for use if the documentation in the record specifies that the intent cannot be determined.

i. Sequelae (Late Effects) of External Cause Guidelines

1) Sequelae external cause codes

Sequela are reported using the external cause code with the 7th character "S" for sequela. These codes should be used with any report of a late effect or sequela resulting from a previous injury.

See Section I.B.10 Sequela (Late Effects)

2) Sequela external cause code with a related current injury

A sequela external cause code should never be used with a related current nature of injury code.

3) Use of sequela external cause codes for subsequent visits

Use a late effect external cause code for subsequent visits when a late effect of the initial injury is being treated. Do not use a late effect external cause code for subsequent visits for follow-up care (e.g., to assess healing, to receive rehabilitative therapy) of the injury when no late effect of the injury has been documented.

j. Terrorism Guidelines

1) Cause of injury identified by the Federal Government (FBI) as terrorism

When the cause of an injury is identified by the Federal Government (FBI) as terrorism, the first-listed external cause code should be a code from category Y38, Terrorism. The definition of terrorism employed by the FBI is found at the inclusion note at the beginning of category Y38. Use additional code for place of occurrence (Y92.-). More than one Y38 code may be assigned if the injury is the result of more than one mechanism of terrorism.

2) Cause of an injury is suspected to be the result of terrorism

When the cause of an injury is suspected to be the result of terrorism a code from category Y38 should not be assigned. Suspected cases should be classified as assault.

3) Code Y38.9, Terrorism, secondary effects

Assign code Y38.9, Terrorism, secondary effects, for conditions occurring subsequent to the terrorist event. This code should not be assigned for conditions that are due to the initial terrorist act.

It is acceptable to assign code Y38.9 with another code from Y38 if there is an injury due to the initial terrorist event and an injury that is a subsequent result of the terrorist event.

k. External cause status

A code from category Y99, External cause status, should be assigned whenever any other external cause code is assigned for an encounter, including an Activity code, except for the events noted below. Assign a code from category Y99, External cause status, to indicate the work status of the person at the time the event occurred. The status code indicates whether the event occurred during military activity, whether a non-military person was at work, whether an individual including a student or volunteer was involved in a non-work activity at the time of the causal event.

A code from Y99, External cause status, should be assigned, when applicable, with other external cause codes, such as transport accidents and falls. The external cause status codes are not applicable to poisonings, adverse effects, misadventures or late effects.

Do not assign a code from category Y99 if no other external cause codes (cause, activity) are applicable for the encounter.

An external cause status code is used only once, at the initial encounter for treatment. Only one code from Y99 should be recorded on a medical record.

Do not assign code Y99.9, Unspecified external cause status, if the status is not stated.