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T21 vs T24.709

T21 (Burn and corrosion of trunk) compared with T24.709 (Corrosion of third degree of unspecified site of unspecified lower limb, except ankle and foot), from the official CMS tabular data.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources

Summary

These codes can be reported together when both conditions are documented, because T24.709 lists T21 under Excludes2, which marks them as distinct conditions.

Official rule
What is different?

The conditions named.T21 is “Burn and corrosion of trunk”; T24.709 is “Corrosion of third degree of unspecified site of unspecified lower limb, except ankle and foot”.

Registry fact

Can these codes be reported together?

Yes, when both are documented.T24.709 lists T21 under Excludes2: “burn and corrosion of hip region (T21.-)”. Excludes2 marks distinct conditions that may both be reported when both are documented.

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes2 relationship?

Yes.T24.709’s tabular entry: “burn and corrosion of hip region (T21.-)”. The note covers T21.

Official ruleGuide: Excludes1 vs Excludes2

Is one a parent or header code?

Both are headers.Both are non-billable headers, and neither contains the other.

Registry fact

Nothing found in 3 other checks; 1 check does not apply
Is there an Excludes1 relationship?

None.Neither entry carries an Excludes1 note that names the other code.

Official rule

Is one more specific?

Not comparable.The codes sit in different categories; specificity is only comparable within one category.

Are there sequencing instructions?

None.Neither entry carries a Code First or Use Additional Code note that names the other.

Official rule

Are there other coding relationships?

None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.

MedCoder-derived

Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels

Can these codes be reported together?

Informational

Excludes2 relationship

T24.709
Corrosion of third degree of unspecified site of unspecified lower limb, except ankle and foot
↔
T21
Burn and corrosion of trunk

What we found

Yes, when both are documented.T24.709 carries an Excludes2 note covering T21: “burn and corrosion of hip region (T21.-)”

Excludes2 marks distinct conditions — both may be reported when both are documented.

What to review

Report both only when the documentation supports both conditions; otherwise report the one documented.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes2 note means the excluded condition is not part of the code above it, but a patient can have both. Report both when both are documented.

Source / rule

CMS ICD-10-CM tabular instructional notes

Official guidance behind these answers

  • Section I.A.12.b — Excludes2 · applies to: Excludes2

    A type 2 Excludes note represents “Not included here.” An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.

    ICD-10-CM Official Guidelines FY2027

Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum

Side by side

Similar descriptions do not make codes interchangeable. The documentation and the official instructions decide which code applies.

Official descriptionDiffers
T21

Burn and corrosion of trunk

T24.709

Corrosion of third degree of unspecified site of unspecified lower limb, except ankle and foot

StatusDiffers
T21
Non-billable header

A header is not reported on a claim; a code beneath it is.

Report instead: T21.00XA, T21.00XD, T21.00XS, T21.01XA, T21.01XD

T24.709
Non-billable header

A header is not reported on a claim; a code beneath it is.

Report instead: T24.709A, T24.709D, T24.709S

Excludes2Differs
T21
  • burns and corrosion of axilla (T22.- with fifth character 4)
  • burns and corrosion of scapular region (T22.- with fifth character 6)
  • burns and corrosion of shoulder (T22.- with fifth character 5)
T24.709
  • burn and corrosion of ankle and foot (T25.-)
  • burn and corrosion of hip region (T21.-)
Code firstDiffers
T21

None at this code

T24.709
  • (T51-T65) to identify chemical and intent
Use additional codeDiffers
Only at T21

No note of its own beyond the shared notes

Only at T24.709
  • external cause code to identify place (Y92)
Shared by both codes (1 note)
  • code from category T31 or T32 to identify extent of body surface involved
CategoryDiffers
T21

Is itself a category

T24.709

T24 Burn and corrosion of lower limb, except ankle and foot

ChapterSame for both

S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)

IncludesDiffers
Only at T21
  • burns and corrosion of hip region
Only at T24.709

No note of its own beyond the shared notes

Shared by both codes (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]
7th characterDiffers
T21
  • The appropriate 7th character is to be added to each code from category T21
T24.709
  • The appropriate 7th character is to be added to each code from category T24

No Excludes1 and Code also note at either code.

Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on. In a row that differs, each code’s own notes are listed under it, and the notes every code shares are listed once beneath them.

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Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources