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T24.721S vs T24.729S

T24.721S (Corrosion of third degree of right knee, sequela) compared with T24.729S (Corrosion of third degree of unspecified knee, sequela), from the official CMS tabular data.

Summary

These codes name the same condition on opposite sides of the body, so the documented side decides which one applies.

MedCoder-derived
What is different?

Title wording.The titles differ in one word, “right” (T24.721S) versus “unspecified” (T24.729S): T24.721S is “Corrosion of third degree of right knee, sequela”; T24.729S is “Corrosion of third degree of unspecified knee, sequela”.

Registry fact

Can these codes be reported together?

One side per condition.T24.721S and T24.729S name the same condition on opposite sides of the body. Same category and title, differing only in which side is affected — the documentation decides which one applies, and a bilateral code is reported only where the code set provides one.

MedCoder-derivedGuide: Laterality coding

Is there an Excludes1 relationship?

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

Official rule

Is there an Excludes2 relationship?

None.Neither entry carries an Excludes2 note that names the other code. T24.721S carries 2 Excludes2 notes and T24.729S carries 2 Excludes2 notes covering other codes; the side-by-side table quotes them.

Official rule

Is one more specific?

Yes.T24.721S’s title names the condition; T24.729S’s title is the unspecified form (“Corrosion of third degree of unspecified knee, sequela”).

MedCoder-derivedGuide: Other vs unspecified (NEC vs NOS)

Is one a parent or header code?

No.Both are billable codes, and neither contains the other.

Registry fact

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?

Yes.Same condition, opposite side. T24.721S and T24.729S name the same condition on opposite sides of the body.

MedCoder-derivedGuide: Laterality coding

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?

Review

Laterality relationship

T24.721S
Right
Corrosion of third degree of right knee, sequela
↔
T24.729S
Unspecified
Corrosion of third degree of unspecified knee, sequela

What we found

Same condition, opposite side.T24.721S and T24.729S name the same condition on opposite sides of the body.

Same category and title, differing only in which side is affected — the documentation decides which one applies, and a bilateral code is reported only where the code set provides one.

What to review

Report the side the documentation names. Where the code set provides a bilateral code and both sides are documented, use it instead of the pair.

Guide: Laterality codingCheck these on a claim

Why it matters

These codes share a category and title and differ only in the side affected. The documentation decides which applies, and a bilateral code is reported only where the code set provides one.

Source / rule

ICD-10-CM tabular list (laterality variant derived from the code title)

Official guidance behind these answers

  • Section I.B.13 — Laterality · applies to: Laterality

    Some ICD-10-CM codes indicate laterality, specifying whether the condition occurs on the left, right or is bilateral. If no bilateral code is provided and the condition is bilateral, assign separate codes for both the left and right side. If the side is not identified in the medical record, assign the code for the unspecified side. When a patient has a bilateral condition and each side is treated during separate encounters, assign the "bilateral" code (as the condition still exists on both sides), including for the encounter to treat the first side. For the second encounter for treatment after one side has previously been treated and the condition no longer exists on that side, assign the appropriate unilateral code for the side where the condition still exists (e.g., cataract surgery performed on each eye in separate encounters). The bilateral code would not be assigned for the subsequent encounter, as the patient no longer has the condition in the previously-treated site. If the treatment on the first side did not completely resolve the condition, then the bilateral code would still be appropriate. When laterality is not documented by the patient’s provider, code assignment for the affected side may be based on medical record documentation from other clinicians. If there is conflicting medical record documentation regarding the affected side, the patient’s provider should be queried for clarification. […]

    ICD-10-CM Official Guidelines FY2026

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

T24.721SCorrosion of third degree of right knee, sequelaT24.729SCorrosion of third degree of unspecified knee, sequela
Billing statusBillableBillable
ClassificationS00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)
DefinitionCorrosion of third degree of right knee, sequela is a billable ICD-10-CM diagnosis code (T24.721S).Corrosion of third degree of unspecified knee, sequela is a billable ICD-10-CM diagnosis code (T24.729S).
7th characterThe appropriate 7th character is to be added to each code from category T24The appropriate 7th character is to be added to each code from category T24
Includes
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]
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]
Excludes2
burn and corrosion of ankle and foot (T25.-)
burn and corrosion of hip region (T21.-)
burn and corrosion of ankle and foot (T25.-)
burn and corrosion of hip region (T21.-)
Code first
(T51-T65) to identify chemical and intent
(T51-T65) to identify chemical and intent
Use additional code
external cause code to identify place (Y92)
code from category T31 or T32 to identify extent of body surface involved
external cause code to identify place (Y92)
code from category T31 or T32 to identify extent of body surface involved

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.

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Derived from the official CMS ICD-10-CM tabular data (FY2026). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources