2027 ICD-10-CM Diagnosis Code T66Radiation sickness, unspecified

ICD-10-CM Codes›S00–T88›T66-T78›T66

ICD-10-CM T66
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

T66 is a non-billable ICD-10-CM category code for radiation sickness, unspecified, so it cannot be submitted on claims. Use a more specific code from this category instead, such as T66.XXXA, T66.XXXD, and T66.XXXS.

Code Identity

ICD-10-CM Code
T66
Billable Status
No — Non-Billable Category
Code Describes
Radiation sickness, unspecified
Short Description
Radiation sickness, unspecified
Same as the full description in the CMS dataset.
Chapter
T66-T78
Other and unspecified effects of external causes

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT66-T78Other and unspecified effects of external causes
CategoryT66Radiation sickness, unspecified
This CodeT66Radiation sickness, unspecified

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Radiation sickness, unspecified (T66). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027, published by CMS and the National Center for Health Statistics.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to T66: its own notes plus those printed at block T66-T78 and Chapter 19. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless 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.-)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • code to identify any retained foreign body, if applicable (Z18.-)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From Block T66-T78 Other and unspecified effects of external causes applies to 456 codes
  • 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

General instructions on how these codes are used.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • 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.

7th Character

Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.

  • The appropriate 7th character is to be added to code T66
Values for category T66 Encounter: Initial, Subsequent, Sequela
  • Ainitial encounter
  • Dsubsequent encounter
  • Ssequela

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name T66, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming T66: its condition is not part of those codes, and both may be reported when the patient has both.

  • Z77.123 Contact with and (suspected) exposure to radon and other naturally occurring radiation
    radiation sickness NOS (T66)

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Patient EducationClinical

Radiation Exposure

Radiation is energy. It travels in the form of energy waves or high-speed particles. Radiation can occur naturally or be man-made. There are two types:

The full article covers:

  • What is radiation?
  • What are the sources of radiation exposure?
  • What are the health effects of radiation exposure?
  • What are the treatments for acute radiation sickness?
  • How can radiation exposure be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About T66Overview

What is the ICD-10 code for radiation sickness, unspecified?

T66 is the ICD-10-CM category for radiation sickness, unspecified, but it is a non-billable header: claims need a more specific code from this category, listed on this page.

Is T66 (Radiation sickness, unspecified) a billable code?

No. This is a category header that groups the codes for radiation sickness, unspecified, and headers cannot be submitted on claims. Claims for radiation sickness, unspecified need a more specific code from this category, such as T66.XXXA, T66.XXXD, and T66.XXXS.

Can T66 be reported with K52.0?

Not as a rule. The Excludes1 note on T66 lists "radiation gastroenteritis and colitis (K52.0)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).