2026 ICD-10-CM Diagnosis Code T25.799ACorrosion of third degree of multiple sites of unspecified ankle and foot, initial encounter
T25.799A is a billable ICD-10-CM diagnosis code for corrosion of third degree of multiple sites of unspecified ankle and foot, 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 928 through 929. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. Coders also document this condition as burn of ankle and foot. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Burn and corrosion, initial encounter.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T25.799A.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Burn of ankle and foot
- Corrosion of ankle and foot
- Corrosion of third degree of ankle and foot
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 ankle and foot (T25). 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.
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.
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Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert T25.799A to ICD-9-CMHistory
Code HistoryHistory
Questions About T25.799AOverview
Is T25.799A a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report corrosion of third degree of multiple sites of unspecified ankle and foot, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in T25.799A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for corrosion of third degree of multiple sites of unspecified ankle and foot, such as an emergency visit or first evaluation.
What MS-DRG does T25.799A group to?
When corrosion of third degree of multiple sites of unspecified ankle and foot, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 928, 929, with relative weights from 3.2208 to 7.1727 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of T25.799A?
Under the General Equivalence Mappings, corrosion of third degree of multiple sites of unspecified ankle and foot, initial encounter converts to ICD-9-CM 945.39 (3rd deg burn leg-mult) and 945.49 (deep 3 deg burn leg-mult). 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.
