T66

ICD-10Non-billable category

Radiation sickness, unspecified

Official ICD-10-CM descriptor (FY2026)

Radiation sickness, unspecified

T66 is a category heading, not a billable code. CMS does not accept it on a claim; report one of the more specific codes beneath it.

Excludes1

Not coded here. An Excludes1 code should never be reported at the same time as the code above it.

  • 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

  • The appropriate 7th character is to be added to code T66

Permitted 7th characters

Ainitial encounter
Dsubsequent encounter
Ssequela

Where this code sits

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Source

ICD-10-CM FY2026. Centers for Medicare & Medicaid Services (CMS) / National Center for Health Statistics (NCHS), “2026 ICD-10-CM Code Descriptions in Tabular Order” (icd10cm_order_2026.txt). Download the original file from cms.gov. Public domain (US Government work). Descriptors, billable flags and instructional notes on this page are reproduced from that file without modification. Krasyn adds no clinical guidance.

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