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Why isn’t “bitten by a dog” a valid diagnosis for coding? Diagnosis vs external cause coding rules explained

Learn what the coding rules are for capturing injuries vs. the cause of the injury and get expert tips on how to properly document for ICD-10 code assignment.

colleagues discussing diagnosis vs external cause coding

At a Glance

  • With medical coding, it’s important to provide specific diagnosis codes for both the injury itself (laceration, contusion, etc.) and the cause of the injury (bitten by a dog, fall)
  • External cause codes help identify how an injury occurred, whether it was accidental or intentional, the location, and the patient’s status at the time of the injury
  • Not including external cause codes or specific injury codes may lead to denied or suspended medical claims

"She was bitten by a dog. How much clearer can I be?”

"He fell. That’s what I wrote on the encounter form. He fell.”

When it comes to injuries, it often seems that physicians and coders speak different languages. Physicians are speaking in English and coders are speaking in — well — code. 

Why aren’t "dog bite icd 10," “bitten by a dog,” or “fall” sufficient for diagnosis code assignment?

Diagnosis coding rules require that when medical practices submit a claim for an injury, the code for the injury itself (laceration, contusion, fracture, sprain) must be listed first, and the code for the cause of the injury (bitten by a dog, fall) be listed second. 

The consequence of only documenting the cause of the injury and not the specific injury itself is that there may never be a principal diagnosis. If the provider simply documents “bitten by a dog” or “fall” the coder is only able to assign the code that describes the cause of the injury. No associated injury code will be assigned resulting in an invalid claim.

As more providers select their own ICD-10 codes in their electronic health records (EHR), it is important that they understand the difference between the codes that capture the injury itself and the codes that capture the cause of the injury. Additionally, understanding the correct sequencing of these codes is imperative since EHR software has a function that will stop the claim before submission if the cause of injury code is used alone or is first. 

As more providers select their own ICD-10 codes in their electronic health records (EHR), it is important that they understand the difference between the codes that capture the injury itself and the codes that capture the cause of the injury. ”

What are external cause codes?

External cause codes are codes that capture the cause of an injury. They are located in chapter 20 of the ICD-10 book titled “External Causes of Morbidity (V00- Y99)." These codes are used with injury codes to identify: 

  • How the injury occurred 
  • Whether it was accidental or intentional 
  • The specific location where it happened 
  • The patient’s status (eg., military or civilian) at the time of the injury

An external cause code from chapter 20 is not assigned if the external cause and intent are already included in a code from another chapter. For example T36.0X1- Poisoning by penicillins, accidental (unintentional) already identifies both the cause (penicillin) and the intent (accidental) and so no additional code from chapter 20 of ICD-10-CM is needed.

External cause codes may be used with any code in the range of A00.0-T88.9, Z00-Z99 that represents a health condition due to an external cause. 

The coder is instructed to use as many external cause codes as is necessary to describe the cause, intent, and place of occurrence. 

External cause codes require a 7th character extension which identifies the episode of care. Specifically A for initial encounter, D for subsequent encounter, and S for sequela. The 7th character for the external cause code must match the 7th character for the associated injury or condition for that encounter.

External causes of morbidity codes may never be used in the first position on the claim form. Use the physical injury first and the external cause second.

Are external cause codes required? ICD-10 requirements 

That is what if the injury code for “contusion” is submitted without the external cause code for “fall”?

Although providers are encouraged to report external cause codes, unless the provider is subject to a state-based mandate for reporting these codes, there is no mandatory requirement. However specific payers often require their use and many payers will deny or suspend the claim when these codes are not included.

What if an external cause ICD-10  code is submitted without an associated injury code? 

That is the external cause code for “fall” is submitted without the injury code for “contusion”? 

The claim will likely result in a medical billing denial. The denial reason will be something like this: Principal diagnosis: invalid; must not be an external cause of injury code.

Correctly submitting the diagnosis codes when the claim is submitted the first time can speed up payments and prevent the need to handle the claim a second time. 

Correctly submitting the diagnosis codes when the claim is submitted the first time can speed up payments and prevent the need to handle the claim a second time. ”

Medical groups that treat injuries should review the use of external cause codes by reading the guidelines related to the codes and reminding clinicians that they are never listed in the first place on an encounter form.

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Betsy Nicoletti, Founder of Codapedia, Speaker, Writer, and Consultant in Coding Education, Billing and Accounts Receivable

Betsy Nicoletti is the author of “The Field Guide to Physician Coding” and founder of Codapedia.com. She developed The Accurate Coding System to help doctors get paid. She simplifies complex coding rules for practitioners and engages physicians in a positive and respectful way, which encourages attention and accuracy in their coding. Besides doing auditing and compliance work, she is a speaker, writer and consultant in coding education, billing and accounts receivable.

Claire Riha, Certified Coding Specialist and Auditing Specialist

Claire Riha is a certified coding specialist who holds both the CCS and RHIT accreditation from AHIMA. She has worked in various capacities within the healthcare industry and has recently launched her own coding education YouTube channel called Medical Coding Clarified. Through this platform, she aims to share her expertise to aspiring coders and industry professionals alike.

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