2026 ICD-10-CM Diagnosis Code S21.042APuncture wound with foreign body of left breast, initial encounter
S21.042A is a billable ICD-10-CM diagnosis code for puncture wound with foreign body 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Open wounds of trunk, initial encounter.
Code Identity
Code Classification
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 S21.042A to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S21.042AOverview
Is S21.042A (Puncture wound with foreign body of left breast) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report puncture wound with foreign body of left breast, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What does the 7th character A in S21.042A mean?
The final character A marks the initial encounter: use it while the patient is receiving active treatment for puncture wound with foreign body of left breast, such as an emergency visit or first evaluation.
What MS-DRG does S21.042A group to?
When puncture wound with foreign body 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 S21.042A?
Under the General Equivalence Mappings, puncture wound with foreign body of left breast, initial encounter converts to ICD-9-CM 879.1 (open wound breast-compl). 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.
