1. Home
  2. ICD-10-CM Codes List
  3. S00–T88
  4. T66-T78
  5. Radiation sickness, unspecified (T66)

Radiation sickness, unspecified (T66)

T66 codes cover radiation sickness when the specific type or cause is not detailed, capturing initial, subsequent, or late effects of exposure to harmful radiation. These codes help document symptoms and complications from radiation exposure without pinpointing specialized conditions.

The ICD-10 code for radiation sickness unspecified (T66) is used to classify general radiation illness cases. Its variations; T66.XXXA for initial encounters, T66.XXXD for follow-up visits, and T66.XXXS for sequela or late effects; encompass a wide range of radiation-induced problems. Commonly associated terms include acute radiation syndrome, radiation sickness, and radiation-induced anemia or infertility, reflecting the diverse health issues caused by overexposure to ionizing radiation. These codes are essential when the detailed diagnosis is not available but the patient’s condition results from radiation effects such as nausea, aplastic anemia, or radiation nephritis. Medical coders use these codes to report radiation toxicity and adverse effects, even when the precise subtype is undetermined, making them critical in radiation injury documentation and healthcare tracking.

Instructional Notations

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.

  • 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 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.

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

7th Character

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

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

Clinical Terms

The following clinical terms provide additional context, helping users better understand the clinical background and common associations for each diagnosis listed in this section. Including related terms alongside ICD-10-CM codes supports coders, billers, and healthcare professionals in improving accuracy, enhancing documentation, and facilitating research or patient education.

Acute Radiation Syndrome

A condition caused by a brief whole body exposure to more than one sievert dose equivalent of radiation. Acute radiation syndrome is initially characterized by ANOREXIA; NAUSEA; VOMITING; but can progress to hematological, gastrointestinal, neurological, pulmonary, and other major organ dysfunction.