T21.4
Corrosion of unspecified degree of trunk
T21.4 is a non-billable ICD-10-CM code header for corrosion of unspecified degree of trunk. Report a more specific code from it instead. It is part of the FY2027 code set, effective October 1, 2026. The more specific codes under it are T21.40 Corrosion of unspecified degree of trunk, unspecified site; T21.41 Corrosion of unspecified degree of chest wall; T21.42 Corrosion of unspecified degree of abdominal wall; T21.43 Corrosion of unspecified degree of upper back and 5 more. Its coding notes include a Code first instruction, a Use additional code instruction and 5 Excludes2 entries.
7th characters
Every code below needs one of these (defined at T21).
The appropriate 7th character is to be added to each code from category T21
- Ainitial encounter
- Dsubsequent encounter
- Ssequela
Guidelines tips
From the FY2027 Official Guidelines. ICD10Ref adds no rules of its own.
The 7th character depends on whether the patient is in active treatment, not on who sees the patient. An aftercare Z code is not used for injury aftercare.
Burns are classified by depth, extent and agent. Burns of the same site and side but different degrees take the highest degree. Non-healing burns are coded as acute burns.
Late effects of burns are coded with 7th character S, and a current burn and a sequela of an old burn can be coded together. An external cause code is used with burns.
Code first
If the underlying condition listed here is present and known, sequence it first.
- (T51-T65) to identify chemical and intent
Use additional code
Add the listed code as a secondary code, if known.
- external cause code to identify place (Y92)
Also from chapter/block level (2 notes)
- code to identify any retained foreign body, if applicable (Z18.-)
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
Also from chapter/block level (2 notes)
- birth trauma (P10-P15)
- obstetric trauma (O70-O71)
Includes
Further defines or gives examples of the content of the category.
- burns and corrosion of hip region
Also from chapter/block level (3 notes)
- burns and corrosions of first degree [erythema]
- burns and corrosions of second degree [blisters][epidermal loss]
- burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss]
Notes
Also from chapter/block level (2 notes)
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
More specific codes under T21.4 9
- T21.40Corrosion of unspecified degree of trunk, unspecified site7th char needed
- T21.41Corrosion of unspecified degree of chest wall7th char needed
- T21.42Corrosion of unspecified degree of abdominal wall7th char needed
- T21.43Corrosion of unspecified degree of upper back7th char needed
- T21.44Corrosion of unspecified degree of lower back7th char needed
- T21.45Corrosion of unspecified degree of buttock7th char needed
- T21.46Corrosion of unspecified degree of male genital region7th char needed
- T21.47Corrosion of unspecified degree of female genital region7th char needed
- T21.49Corrosion of unspecified degree of other site of trunk7th char needed