Radiation sickness, unspecified (T66) ICD-10-CM
The T66 code range covers radiation sickness, unspecified with 4 ICD-10-CM diagnosis codes. 3 of them are billable and valid for claim submission in fiscal year 2027, and the category headers group them but cannot themselves be billed.
Type 1 Excludes
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.
- 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
7th Character Note
Certain ICD-10-CM categories have applicable 7th characters. The applicable 7th character is required for all codes within the category, or as the notes in the Tabular List instruct. The 7th character must always be the 7th character in the data field. If a code that requires a 7th character is not 6 characters, a placeholder X must be used to fill in the empty characters.
- The appropriate 7th character is to be added to code T66
7th Character
Indicates that a seventh character is to be assigned to codes in a subcategory.
- A - initial encounter
- D - subsequent encounter
- S - sequela
Codes in the T66 Range 4 codes · 3 billable
About the T66 Code Range
Radiation sickness is an effect of radiation. T66 does not distinguish between types of radiation sickness.
Its subdivisions differ by encounter: T66.XXXA is initial, T66.XXXD is subsequent, and T66.XXXS is for a sequela, an effect that remains afterward. The seventh character marks that distinction with A, D, or S.
Questions About This Page
How many billable codes are in the T66 range?
Of the 4 codes in this range, 3 are billable and valid for claim submission from October 1, 2026 through September 30, 2027. Category header codes group them but cannot be reported on claims.
What does the T66 range classify?
The range classifies radiation sickness, unspecified. Each code links to its own reference page with billing status, MS-DRG grouping, coding notes, and clinical information.
Related References
Source: CMS FY 2027 ICD-10-CM Tabular List and order file, effective October 1, 2026 through September 30, 2027.
