2026 ICD-10-CM Diagnosis Code S21.002AUnspecified open wound of left breast, initial encounter
S21.002A is a billable ICD-10-CM diagnosis code for unspecified open wound of left breast, 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 604 through 605, 963 through 965. Coders also document this condition as open wound of left breast. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Open wounds of trunk, initial encounter.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Open wound of left breast
Coding GuidelinesGuidance
The appropriate 7th character is to be added to each code from block Open wound of thorax (S21). 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
Breast Diseases
Breast diseases include various conditions and changes in your breast. Most women experience breast changes at some time. Your age, hormone levels, and medicines you take may cause lumps, bumps, and discharges of fluids that are not breast milk.
The full article covers:
- What are breast diseases?
- What are the symptoms of breast disease?
- How are breast diseases diagnosed?
- What are the treatments for breast disease?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert S21.002A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S21.002AOverview
What is the ICD-10 code for unspecified open wound of left breast, initial encounter?
The ICD-10-CM code for unspecified open wound of left breast, initial encounter is S21.002A (sometimes written as S21002A). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
Is S21.002A (Unspecified open wound of left breast) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report unspecified open wound of left breast, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in S21.002A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for unspecified open wound of left breast, such as an emergency visit or first evaluation.
What MS-DRG does S21.002A group to?
When unspecified open wound of left breast, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 604, 605, 963, 964, 965, with relative weights from 0.9160 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of S21.002A?
Under the General Equivalence Mappings, unspecified open wound of left breast, initial encounter converts to ICD-9-CM 879.0 (open wound of breast). The mapping is approximate, so confirm the match fits the documentation.
