2021 ICD-10-CM Code T66

Radiation sickness, unspecified

Version 2021

Not Valid for Submission

ICD-10:T66
Short Description:Radiation sickness, unspecified
Long Description:Radiation sickness, unspecified

Code Classification

  • Injury, poisoning and certain other consequences of external causes (S00–T98)
    • Other and unspecified effects of external causes (T66-T78)
      • Radiation sickness, unspecified (T66)

T66 is a non-specific and non-billable diagnosis code code, consider using a code with a higher level of specificity for a diagnosis of radiation sickness, unspecified. The code is not specific and is NOT valid for the year 2021 for the submission of HIPAA-covered transactions. Category or Header define the heading of a category of codes that may be further subdivided by the use of 4th, 5th, 6th or 7th characters.

Unspecified diagnosis codes like T66 are acceptable when clinical information is unknown or not available about a particular condition. Although a more specific code is preferable, unspecified codes should be used when such codes most accurately reflect what is known about a patient's condition. Specific diagnosis codes should not be used if not supported by the patient's medical record.

Coding Guidelines

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

Tabular List of Diseases and Injuries

The Tabular List of Diseases and Injuries is a list of ICD-10 codes, organized "head to toe" into chapters and sections with coding notes and guidance for inclusions, exclusions, descriptions and more. The following references are applicable to the code T66:


Type 1 Excludes

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.

7th Character Note

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.

7th Character

7th Character
Indicates that a seventh character is to be assigned to codes in a subcategory.

Index to Diseases and Injuries

The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10 code(s). The following references for the code T66 are found in the index:

Clinical Information

Information for Patients


Radiation Exposure

What is radiation?

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:

What are the sources of radiation exposure?

Background radiation is all around us all the time. Most of it forms naturally from minerals. These radioactive minerals are in the ground, soil, water, and even our bodies. Background radiation can also come from outer space and the sun. Other sources are man-made, such as x-rays, radiation therapy to treat cancer, and electrical power lines.

What are the health effects of radiation exposure?

Radiation has been around us throughout our evolution. So our bodies are designed to deal with the low levels we're exposed to every day. But too much radiation can damage tissues by changing cell structure and damaging DNA. This can cause serious health problems, including cancer.

The amount of damage that exposure to radiation can cause depends on several factors, including

Being exposed to a lot of radiation over a short period of time, such as from a radiation emergency, can cause skin burns. It may also lead to acute radiation syndrome (ARS, or "radiation sickness"). The symptoms of ARS include headache and diarrhea. They usually start within hours. Those symptoms will go away and the person will seem healthy for a little while. But then they will get sick again. How soon they get sick again, which symptoms they have, and how sick they get depends on the amount of radiation they received. In some cases, ARS causes death in the following days or weeks.

Exposure to low levels of radiation in the environment does not cause immediate health effects. But it can slightly increase your overall risk of cancer.

What are the treatments for acute radiation sickness?

Before they start treatment, health care professionals need to figure out how much radiation your body absorbed. They will ask about your symptoms, do blood tests, and may use a device that measures radiation. They also try get more information about the exposure, such as what type of radiation it was, how far away you were from the source of the radiation, and how long you were exposed.

Treatment focuses on reducing and treating infections, preventing dehydration, and treating injuries and burns. Some people may need treatments that help the bone marrow recover its function. If you were exposed to certain types of radiation, your provider may give you a treatment that limits or removes the contamination that is inside your body. You may also get treatments for your symptoms.

How can radiation exposure be prevented?

There are steps you can take to prevent or reduce radiation exposure:

Environmental Protection Agency


[Learn More in MedlinePlus]

Code History

  • FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016 (First year ICD-10-CM implemented into the HIPAA code set)