External cause codes in the International Classification of Diseases, 10th Edition (ICD-10) have been the source of much hilarity—and considerable concern. After all, who would ever consider the need for a code to report the following incidents?

• injury due to depth charge
• accident involving spacecraft injuring occupant of spacecraft
• animal-drawn vehicle accident injuring occupant of streetcar

But these are not ICD-10 codes at all; they are the wild ICD-9 external cause codes that you might not have known existed for all these years because they simply never came to your attention.

External cause codes are used to classify environmental events and circumstances as the cause of injuries and other adverse effects. They are found in chapter 20 of the ICD-10-CM book and are a supplementary chapter in the ICD-9-CM book.

Although ICD-9 contained approximately 1,100 external cause codes, ICD-10 has about 9,700 of such codes, due to the “granularity” and the expanded detail required by ICD-10. For example, Table 1 shows how a single external cause code in ICD-9 becomes nine separate codes in ICD-10.

Keep in mind that each of the nine codes shown for ICD-10 has two additional codes—one for subsequent visit for routine healing (seventh character D) and one for sequelae (seventh character S). In other words, one ICD-9 code became 27 ICD-10 codes.

The ICD-9 external cause code categories were reorganized and expanded in ICD-10—from 25 categories to 29 categories (Table 2). For example, although 13 ICD-9 codes address incidents of terrorism, ICD-10 has more than 105 codes addressing terrorist acts causing injuries.

Laughter is the best medicine
Injuries from animals have provided tremendous opportunity for folly as the media discusses ICD-10 codes. A physician may be required to evaluate a patient who was bitten, scratched, struck, pecked, or crushed by any one of 37 living creatures, from a mouse to a sea lion (codes W50.01-W61.91). If none of those descriptions applies, the provider could report “other contact” with the same 37 beasts.

Injuries inflicted by other humans are completely different; in these circumstances, ICD-10 addresses intent. A surgeon could be asked to evaluate an accidental hit, strike, kick, twist, scratch, or bite by another human being (all separate codes W50.0-W50.4) or a patient who sustained an assault by human bite (Y0V.1). Is it any wonder that this chapter of ICD-10 provides fodder for laughter?

The truth is that the use of the codes describing external causes of morbidity will still be voluntary. The following joint statement was released by the American Health Information Management Association, the American Hospital Association, the Centers for Medicare & Medicaid Services, and the National Center for Health Statistics:

Just as with ICD-9-CM, 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. If a provider has not been reporting ICD-9-CM external cause codes, the provider will not be required to report ICD-10-CM codes in Chapter 20, unless a new state or payer-based requirement regarding the reporting of these codes is instituted. Such a requirement would be independent of ICD-10-CM implementation. 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.

External cause codes may be required by workers’ compensation and third-party liability payers to describe a work-related incident or a motor vehicle accident. This practice is likely to continue with conversion to ICD-10.

Some of the more bizarre external cause codes under ICD-10 may continue to serve as a source of amusement, but coders understand that the concept of external cause codes is not a new one. Savvy practice managers will use the ICD-10 implementation delay to identify the ICD-9 external cause codes that are occasionally requested by specific payers and to ensure that the documentation sufficient to support their use is complete.

Margaret M. Maley, BSN, MS, is a senior consultant with KarenZupko & Associates, Inc., who focuses on CPT and ICD-10 coding education for orthopaedic practices.