When that angry little neighbor dog decides to take a bite out of someone’s child, and you are a medical coder, you will need to be able to assign the correct code. This coding scenario involves external cause codes and the bite from the angry dog.

an angry dog and assigning external cause code for dog bite

Question: A 7-year-old girl was playing yesterday with her next-door neighbor, and they were running around after each other with squirt guns. The neighbor’s little dog must have felt the 7-year-old was threatening the other girl, and the dog bit her on the leg. On examination, she has multiple jagged bites and a painful open wound in the right lower leg. Assign the external cause code for the dog bite.


W54.0XXA, Bitten by dog, initial encounter

We are not being asked to assign for the open bite here. Instead, we need to assign the external cause code, which is a secondary code that can be found in Chapter 20, External causes of morbidity. This code explains the cause of the injury.

Bitten By Dog

Locate and Verify

Looking in the ICD-10-CM External Cause of Injuries Index, see Bite, bitten by, dog W54.0.

Verified in the Tabular, W54.0 refers to Bitten by dog. However, this code is unreportable, because it requires a 7th character.

W54.0XXA should be assigned to show it is an initial encounter and the patient is receiving active treatment.

If this were a subsequent encounter, “D” would be the 7th character provided; a sequela would be reported with “S” as the 7th character.

Coding Guidelines for External Causes

According to the ICD-10-CM coding guidelines, external cause codes are used to identify the cause, intent, place where the patient was when injured, patient’s status, and activity being performed at the time.

The following instructions are provided at W54:

Includes: contact with saliva, feces, or urine of dog

Excludes1: Toxic effect of contact with venomous animals and plants (T63.-)

Notes at V00-Y99:

“This chapter permits the classification of environmental events and circumstances as the cause of injury and other adverse effects. Where a code from this section is applicable, it is intended that it shall be used secondary to a code from another chapter of the Classification indicating the nature of the condition. Most often, the condition will be classifiable to Chapter 19, Injury, poisoning and certain other consequences of external causes (S00-T88). Other conditions that may be stated to be due to external causes are classified in Chapters I to XVIII. For these conditions, codes from Chapter 20 should be used to provide additional information as to the cause of the condition.”

Takeaway: External cause codes are never reported alone and they are never reported as primary or principal. They help tell the story as to the cause of the principal diagnosis.

This post has been updated to reflect the FY 2021 ICD-10-CM coding guidelines.