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T21.79XS ICD-10-CM Code: Corrosion of third degree of other site of trunk, sequela

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

7th character
Required — see the character table on this page
Tabular directives
4 inclusion terms · 3 Excludes2 · 2 use-additional codes · 1 code-first instruction

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 604 — TRAUMA TO THE SKIN, SUBCUTANEOUS TISSUE AND BREAST WITH MCC (MDC 09)
  • MS-DRG 605 — TRAUMA TO THE SKIN, SUBCUTANEOUS TISSUE AND BREAST WITHOUT MCC (MDC 09)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for T21.79XS in the official ICD-10-CM tabular list, quoted as published.

Notes without a marker are published on T21.79XS itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

  • burns and corrosion of hip region inherited from T21
  • burns and corrosions of first degree [erythema] inherited from T20-T25
  • burns and corrosions of second degree [blisters][epidermal loss] inherited from T20-T25
  • burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss] inherited from T20-T25

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Source: inherited from T21

Code First

Underlying conditions that must be sequenced before this code.

  • (T51-T65) to identify chemical and intent

Source: inherited from T21.7

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • external cause code to identify place (Y92) inherited from T21.7
  • Use additional code from category T31 or T32 to identify extent of body surface involved inherited from T20-T25

7th Character Guide

"The appropriate 7th character is to be added to each code from category T21"

  • A — initial encounter
  • D — subsequent encounter
  • S — sequela (this page’s code)

How the encounter character is assigned. “Initial encounter” means the patient is receiving active treatment for the condition — it is not limited to the first visit, and a different or new provider giving active treatment still assigns it. “Subsequent encounter” covers care during the healing or recovery phase after active treatment. “Sequela” is for complications or conditions that arise as a direct result of the original condition.

ICD-10-CM Official Guidelines for Coding and Reporting, Section I.C.19.a (paraphrased by MedCoder).

Variant codes in this family

T21.79XA, T21.79XD, T21.79XS

Character meanings are CMS's official 7th-character extensions for this family, as carried in each variant code's official description; variant codes are registry rows. The explanation of how the encounter character is assigned is MedCoder editorial, distinct from the official content above it.

Code Overview

Corrosion of third degree of other site of trunk, sequela is a billable ICD-10-CM diagnosis code (T21.79XS).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

  1. A 7th character applies in this family. Confirm the documented encounter matches the character assigned. See the official 7th-character definitions and this code’s variants
  2. Sequencing: 1 Code First instruction — the underlying condition is sequenced before this code when present. See the Code First notes
  3. 2 Use Additional Code instructions — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
  4. 3 Excludes2 entries — those conditions are not part of this code and may be reported additionally when documented. See the Excludes2 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

  • No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

Other codes that name T21.79XS or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 2 Excludes1 notes: T07 — Unspecified multiple injuries (via T21.-), T66 — Radiation sickness, unspecified (via T21.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 123 Excludes2 notes: S00 — Superficial injury of head (via T21.-), S00-S09 — Injuries to the head (S00-S09) (via T21.-), S01 — Open wound of head (via T21.-), S02 — Fracture of skull and facial bones (via T21.-), S03 — Dislocation and sprain of joints and ligaments of head (via T21.-), S04 — Injury of cranial nerve (via T21.-), S05 — Injury of eye and orbit (via T21.-), S06 — Intracranial injury (via T21.-), S07 — Crushing injury of head (via T21.-), S08 — Avulsion and traumatic amputation of part of head (via T21.-), S09 — Other and unspecified injuries of head (via T21.-), S10 — Superficial injury of neck (via T21.-), S10-S19 — Injuries to the neck (S10-S19) (via T21.-), S11 — Open wound of neck (via T21.-), S12 — Fracture of cervical vertebra and other parts of neck (via T21.-), S13 — Dislocation and sprain of joints and ligaments at neck level (via T21.-), S14 — Injury of nerves and spinal cord at neck level (via T21.-), S15 — Injury of blood vessels at neck level (via T21.-), S16 — Injury of muscle, fascia and tendon at neck level (via T21.-), S17 — Crushing injury of neck (via T21.-), +103 more.

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

MS-DRG Grouper Relationships (FY2026)

Not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity.

Potential MS-DRG participation — not a DRG assignment.

Named in the grouper logic of 2 MS-DRGs: DRG 604 (MDC 09), DRG 605 (MDC 09).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):INJ073 — Injury, sequela (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same injury, other encounter phase

Same injury, coded at a different phase of treatment via the 7th character.

T21.79XA — Corrosion of third degree of other site of trunk, initial encounterCompare T21.79XS vs T21.79XA →, T21.79XD — Corrosion of third degree of other site of trunk, subsequent encounter

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Injury, sequela).

+7578 more

Contextual Map

Every relationship of T21.79XS in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run T21.79XS with these 10 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Excludes2 notes (123)

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

  • MDC 09 — Diseases and Disorders of the Skin, Subcutaneous Tissue and Breast[MDC crossing]: “Diseases and Disorders of the Skin, Subcutaneous Tissue and Breast — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 7,376 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Nearest codes (40)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Common coding questions

Does T21.79XS require a 7th character?

Yes. The appropriate 7th character is to be added to each code from category T21.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Corrosion of third degree of other site of trunk, sequela

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027 (effective October 1, 2026), and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to T21.79XS in its code family, with their registry titles.

View all codes in the T21 family