Coding and coverage · ICD-10-CM

T66

T66.XXXS Radiation sickness, unspecified, sequela

BillableNo payment HCCChapter 19

7th character S: sequela

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Instructional notes

Chapter 19

Excludes2Not included here: the patient may have both; report both when both are present.
Use additional codeAdd a second code for the full picture.
  • code to identify any retained foreign body, if applicable (Z18.-)
Notes
  • Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
  • The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.

T66

Excludes1Not coded here: never report with this code, except when the two conditions are unrelated.
  • 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 charactersThe appropriate 7th character is to be added to code T66
  • A initial encounter
  • D subsequent encounter
  • S sequela

Chapter 19: Injury, poisoning and certain other consequences of external causes · T07-T88 Injury, poisoning and certain other consequences of external causes (T07-T88)

Source: ICD-10-CM FY 2027 code descriptions and tabular list (CMS and CDC National Center for Health Statistics), effective 2026-10-01 through 2027-09-30 · CMS ICD-10 files. HCC mapping: CMS-HCC V28, payment year 2027. As of 2026-11-04.

Coverage and payment depend on the claim details; confirm with the Medicare Administrative Contractor.