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T20 vs T66.XXXA

T20 (Burn and corrosion of head, face, and neck) compared with T66.XXXA (Radiation sickness, unspecified, initial encounter), 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 should not be reported together because T66.XXXA’s tabular entry lists T20 under Excludes1.

Official rule
What is different?

The conditions named and billing status.T20 is “Burn and corrosion of head, face, and neck”; T66.XXXA is “Radiation sickness, unspecified, initial encounter”. T20 is a non-billable header; T66.XXXA is billable.

Registry fact

Can these codes be reported together?

No.T66.XXXA’s entry carries an Excludes1 note covering T20: “burns (T20-T31)”. Both may be reported only when the documentation shows the two conditions are unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes1 relationship?

Yes.T66.XXXA’s tabular entry: “burns (T20-T31)”. The note covers T20.

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes2 relationship?

None.Neither entry carries an Excludes2 note that names the other code. T20 carries 3 Excludes2 notes covering other codes; the side-by-side table quotes them.

Official rule

Is one more specific?

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

Is one a parent or header code?

One is a header.T20 is a non-billable header, but T66.XXXA is not one of its subdivisions.

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?

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?

Excludes1 — generally not reported together

Excludes1 conflict

T66.XXXA
Radiation sickness, unspecified, initial encounter
↔
T20
Burn and corrosion of head, face, and neck

What we found

No — do not report together.T66.XXXA carries an Excludes1 note covering T20: “burns (T20-T31)”

Sole exception: when the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

What to review

Report one of the two. Both may be reported only when the documentation shows the two conditions are unrelated to each other.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes1 note means the two conditions are not ordinarily reported together for the same encounter, because the classification treats them as mutually exclusive forms of the same condition. The documented exception is when the two conditions are unrelated to each other.

Source / rule

CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a

Official guidance behind these answers

  • Section I.A.12.a — Excludes1 · applies to: Excludes1

    A type 1 Excludes note is a pure excludes note. It means “NOT CODED HERE!” An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition. An exception to the Excludes1 definition is the circumstance when the two conditions are unrelated to each other. If it is not clear whether the two conditions involving an Excludes1 note are related or not, query the provider. For example, code F45.8, Other somatoform disorders, has an Excludes1 note for "sleep related teeth grinding (G47.63)," because "teeth grinding" is an inclusion term under F45.8. Only one of these two codes should be assigned for teeth grinding. However psychogenic dysmenorrhea is also an inclusion term under F45.8, and a patient could have both this condition and sleep related teeth grinding. In this case, the two conditions are clearly unrelated to each other, and so it would be appropriate to report F45.8 and G47.63 together.

    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

T20Burn and corrosion of head, face, and neckT66.XXXARadiation sickness, unspecified, initial encounter
Billing statusNon-billable header

Report instead: T20.00XA, T20.00XD, T20.00XS, T20.011A, T20.011D

Billable
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)
DefinitionBurn and corrosion of head, face, and neck is a non-billable ICD-10-CM category code (T20).Radiation sickness, unspecified, initial encounter is a billable ICD-10-CM diagnosis code (T66.XXXA).
7th characterThe appropriate 7th character is to be added to each code from category T20The appropriate 7th character is to be added to code T66
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]
—
Excludes1—
specified adverse effects of radiation, such as:
burns (T20-T31)
leukemia (C91-C95)
radiation gastroenteritis and colitis (K52.0)
radiation pneumonitis (J70.0)
radiation related disorders of the skin and subcutaneous tissue (L55-L59)
sunburn (L55.-)
Excludes2
burn and corrosion of ear drum (T28.41, T28.91)
burn and corrosion of eye and adnexa (T26.-)
burn and corrosion of mouth and pharynx (T28.0)
—
Use additional code
code from category T31 or T32 to identify extent of body surface involved
—
Code also—
, if applicable, place of occurrence, such as:
highway rest stop (Y92.523)
school (private) (public) (state) as the place of occurrence of the external cause (Y92.21-)
service areas as the place of occurrence of the external cause (Y92.52-)
single-family non-institutional (private) house as the place of occurrence of the external cause (Y92.01-)
transport vehicle as the place of occurrence of the external cause (Y92.81-)

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 (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources