Is ICD-10-CM code T66 billable?

No, T66 (Radiation sickness, unspecified) is a non-billable ICD-10-CM code. It must be coded to a more specific subcategory before it can be used for reimbursement.

What chapter does ICD-10-CM code T66 belong to?

T66 belongs to Chapter 19 of the ICD-10-CM tabular list: S00–T88 (Injury, Poisoning and Certain Other Consequences of External Causes).

T66Not billable, use a more specific code below

Radiation sickness, unspecified

In Other and unspecified effects of external causes (T66-T78), chapter 19: Injury, Poisoning and Certain Other Consequences of External Causes

3 billable codes under T66: none are a CC or MCC; none map to an HCC.

Also indexed as: Effect, infrared NOS; Effect, radiation NOS; Effect, ultraviolet NOS; Irradiation effects; Radiation, effects NOS; Radiation, sickness NOS; Sickness, radiation

Instructional notes

Excludes1: not coded here, use a different code

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.-)

Also applies, from Other and unspecified effects of external causes (T66-T78)

These notes sit on T66-T78 and apply to every code under it, including T66.

Code also: add a code for this too, order depends on the encounter

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-)

Official coding guidelines

From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.

Covers 7th character use and coding of injuries, fractures, burns, drug and toxic effects, abuse and neglect, and complications of care (S00-T88).

Application of 7th Characters in Chapter 19 (page 77)
Coding of Injuries (page 78)
Coding of Traumatic Fractures (page 79)
Coding of Burns and Corrosions (page 80)
Adverse Effects, Poisoning, Underdosing and Toxic Effects (page 82)
Adult and child abuse, neglect and other maltreatment (page 85)
Complications of care (page 85)

Read Section I.C.19 (page 77)

All codes under T66

T66 can't be used on a claim. Pick a billable code below; grey headings group them.

T66 MS-DRGs

As the principal diagnosis, the billable codes under T66 group to MS-DRG 922, 923, 949, or 950 (v44.0). Which one applies depends on procedures performed, secondary diagnoses (CC/MCC), and the patient's age and discharge status.

DRG 922 Other Injury, Poisoning and Toxic Effect Diagnoses with MCC (2 of 3 codes)
DRG 923 Other Injury, Poisoning and Toxic Effect Diagnoses without MCC (2 of 3 codes)
DRG 949 Aftercare with CC/MCC (1 of 3 codes)
DRG 950 Aftercare without CC/MCC (1 of 3 codes)

Other codes that refer to T66

Notes on these codes point to T66.

Z77.123 Excludes2: radiation sickness NOS (T66)

About the condition

Plain-language background from MedlinePlus (National Library of Medicine), not coding guidance.

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:

Code history

Valid since FY2016, when ICD-10-CM took effect on October 1, 2015. No changes since.