2026 ICD-10-CM Diagnosis Code T33.40XASuperficial frostbite of unspecified arm, initial encounter

ICD-10-CM Codes›S00–T88›T33-T34›T33

ICD-10-CM T33.40XA
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T33.40XA is a billable ICD-10-CM diagnosis code for superficial frostbite of unspecified arm, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 922 through 923. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. Coders also document this condition as frostbite of upper arm. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Effect of other external causes, initial encounter.

Code Identity

ICD-10-CM Code
T33.40XA
Billable Status
Yes — Valid for Submission
Code Describes
Superficial frostbite of unspecified arm, initial encounter
Short Description
Superficial frostbite of unspecified arm, initial encounter
Same as the full description in the CMS dataset.
Parent Code
T33.40
Superficial frostbite of unspecified arm

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT33-T34Frostbite
CategoryT33Superficial frostbite
This CodeT33.40XASuperficial frostbite of unspecified arm, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T33.40XA.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Frostbite of upper arm
  • Frostbite of upper limb
  • Superficial frostbite
  • Superficial frostbite of upper arm
  • Superficial frostbite of upper limb

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Superficial frostbite (T33). 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 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ021
Effect of other external causes, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Frostbite

Frostbite is an injury to the body that is caused by freezing. It most often affects the nose, ears, cheeks, chin, fingers, or toes. Frostbite can permanently damage the body, and severe cases can lead to amputation.

Read the full article at MedlinePlus

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

Convert T33.40XA to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
991.3 Frostbite NEC/NOS
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T33.40XAOverview

Is T33.40XA (Superficial frostbite of unspecified arm) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report superficial frostbite of unspecified arm, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T33.40XA mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for superficial frostbite of unspecified arm, such as an emergency visit or first evaluation.

What MS-DRG does T33.40XA group to?

When superficial frostbite of unspecified arm, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 922, 923, with relative weights from 1.0177 to 1.7494 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of T33.40XA?

Under the General Equivalence Mappings, superficial frostbite of unspecified arm, initial encounter converts to ICD-9-CM 991.3 (frostbite NEC/NOS). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.