2027 ICD-10-CM Diagnosis Code T23.412ACorrosion of unspecified degree of left thumb (nail), initial encounter
T23.412A is a billable ICD-10-CM diagnosis code for corrosion of unspecified degree of left thumb (nail), 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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 935. Coders also document this condition as burn of left thumb. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Burn and corrosion, initial encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Burn of left thumb
- Chemical burn of hand
- Chemical burn of left hand
- Chemical burn of left thumb
- Chemical burn of thumb
Coding GuidelinesGuidance
The ICD-10-CM makes a distinction between burns and corrosions. The burn codes are for thermal burns, except sunburns, that come from a heat source, such as a fire or hot appliance. The burn codes are also for burns resulting from electricity and radiation. Corrosions are burns due to chemicals. The guidelines are the same for burns and corrosions.
Sequence first the code that reflects the highest degree of burn when more than one burn is present.
- When the reason for the admission or encounter is for treatment of external multiple burns, sequence first the code that reflects the burn of the highest degree.
- When a patient has both internal and external burns, the circumstances of admission govern the selection of the principal diagnosis or first-listed diagnosis.
- When a patient is admitted for burn injuries and other related conditions such as smoke inhalation and/or respiratory failure, the circumstances of admission govern the selection of the principal or first-listed diagnosis.
Current burns (T20-T25) are classified by depth, extent and by agent (X code). Burns are classified by depth as first degree (erythema), second degree (blistering), and third degree (full-thickness involvement).
Classify burns of the same local site (three-character category level, T20-T28) but of different degrees to the subcategory identifying the highest degree recorded in the diagnosis.
The appropriate 7th character is to be added to each code from block Burn and corrosion of wrist and hand (T23). 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 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T23.412A: its own notes plus those printed at T23.4, T23, block T20-T32, block T20-T25, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- burns (thermal) from electrical heating appliances
- burns (thermal) from electricity
- burns (thermal) from flame
- burns (thermal) from friction
- burns (thermal) from hot air and hot gases
- burns (thermal) from hot objects
- burns (thermal) from lightning
- burns (thermal) from radiation
- chemical burn [corrosion] (external) (internal)
- scalds
- burns and corrosions of first degree [erythema]
- burns and corrosions of second degree [blisters][epidermal loss]
- burns and corrosions of third degree [deep necrosis of underlying tissue] [full- thickness skin loss]
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Code First
The underlying condition named in the note is sequenced before this code.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- external cause code to identify place (Y92)
- code to identify any retained foreign body, if applicable (Z18.-)
Notes
General instructions on how these codes are used.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T23
- Ainitial encounter this code
- Dsubsequent encounter
- Ssequela
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T23.412A, its category, or a range that includes it.
Excludes2 1
These codes carry an Excludes2 note naming T23.412A: its condition is not part of those codes, and both may be reported when the patient has both.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Burns
A burn is damage to your body's tissues caused by heat, chemicals, electricity, sunlight, or radiation. Scalds from hot liquids and steam, building fires and flammable liquids and gases are the most common causes of burns. Another kind is an inhalation injury, caused by breathing smoke.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T23.412A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T23.412AOverview
Is T23.412A (Corrosion of unspecified degree of left thumb (nail)) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report corrosion of unspecified degree of left thumb (nail), initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character A in T23.412A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for corrosion of unspecified degree of left thumb (nail), such as an emergency visit or first evaluation.
What MS-DRG does T23.412A group to?
When corrosion of unspecified degree of left thumb (nail), initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 935 (Non-Extensive Burns), which carries a relative weight of 2.4232. Higher weights mean higher Medicare reimbursement.
Does T23.412A need an additional code?
When the condition applies, yes. The Use Additional Code note at T23.4, which applies to T23.412A, reads: external cause code to identify place (Y92). The additional code is reported after T23.412A.
What is the ICD-9 equivalent of T23.412A?
Under the General Equivalence Mappings, corrosion of unspecified degree of left thumb (nail), initial encounter converts to ICD-9-CM 944.02 (burn NOS thumb). The mapping is approximate, so confirm the match fits the documentation.
