Skip to main content

T66.XXXD ICD-10-CM Code: Radiation sickness, unspecified, subsequent encounter

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Inpatient Payment Groups (MS-DRG)

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43.0, Appendix B.

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Official Registry Overview & Definition

Radiation sickness, unspecified, subsequent encounter is a billable ICD-10-CM diagnosis code (T66D).

Official Tabular Instructional Notes

Sequencing, inclusion, and exclusion notes published for T66.XXXD in the official ICD-10-CM tabular list.

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Code Also

Additional codes that may be required to fully describe the encounter.

  • Code also, 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-)

Frequently Compared Codes

The official Excludes notes on T66.XXXD name these codes. Each comparison page covers when the two can — or must not — be reported together.

Change history

No changes recorded for this code — unchanged since the FY2016 baseline of the change ledger.

Verify Before Coding

  • No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim.

Contextual Map

Every relationship of T66.XXXD in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Hierarchy

  • S00-T88 — Chapter 19: Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88) (S00-T88) [Hierarchy]
  • T66-T78 — Other and unspecified effects of external causes [Hierarchy]

Clinical classification (CCSR)

  • INJ058 — Effect of other external causes, subsequent encounter [CCSR]

Potential MS-DRG

  • DRG 949 — AFTERCARE WITH CC/MCC [MS-DRG]: “AFTERCARE WITH CC/MCC (MDC 23)”
  • DRG 950 — AFTERCARE WITHOUT CC/MCC [MS-DRG]: “AFTERCARE WITHOUT CC/MCC (MDC 23)”

MDC crossing · procedures (1235)

  • MDC 23 — Factors Influencing Health Status and Other Contacts with Health Services [MDC crossing]: “Factors Influencing Health Status and Other Contacts with Health Services — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs.”
  • F003GKZ — Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Audiovisual Equipment [Same-MDC procedure]: “Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Audiovisual Equipment — grouped in MDC 23, the procedure side of this code's crossing.” · check together
  • F003GMZ — Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Augmentative / Alternative Communication Equipment [Same-MDC procedure]: “Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Augmentative / Alternative Communication Equipment — grouped in MDC 23, the procedure side of this code's crossing.” · check together
  • F003GPZ — Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Computer [Same-MDC procedure]: “Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Computer — grouped in MDC 23, the procedure side of this code's crossing.” · check together
  • F003GYZ — Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Other Equipment [Same-MDC procedure]: “Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body using Other Equipment — grouped in MDC 23, the procedure side of this code's crossing.” · check together
  • F003GZZ — Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body [Same-MDC procedure]: “Communicative/Cognitive Integration Skills Assessment of Neurological System - Whole Body — grouped in MDC 23, the procedure side of this code's crossing.” · check together
  • and 1230 more

Nearest codes

  • T66 — Radiation sickness, unspecified [Sibling]
  • T66.XXXA — Radiation sickness, unspecified, initial encounter [Sibling]
  • T66.XXXS — Radiation sickness, unspecified, sequela [Sibling]

Relationships & Classification

Clinical classification (AHRQ CCSR):INJ058 — Effect of other external causes, subsequent encounter (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Potential MS-DRG Relationships (FY2026)

Not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity.

Named in the grouper logic of 2 MS-DRGs: DRG 949 (MDC 23), DRG 950 (MDC 23).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Frequently Asked Questions (FAQ) & Clinical Guidance

Does T66.XXXD require a 7th character?

Yes. The appropriate 7th character is to be added to code T66.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to T66.XXXD in its code family, with their registry titles.

  • T66 — Radiation sickness, unspecified
  • T66.XXXA — Radiation sickness, unspecified, initial encounter
  • T66.XXXS — Radiation sickness, unspecified, sequela

View all codes in the T66 family