2026 ICD-10-CM Diagnosis Code Z42.1Encounter for breast reconstruction following mastectomy
Z42.1 is a billable ICD-10-CM diagnosis code for encounter for breast reconstruction following mastectomy. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 606 through 607. The code is restricted by the Medicare Code Editor to adult patients (age 15 through 124) and exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Encounter for prophylactic or other procedures.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for Z42.1.
Present on Admission (POA)Billing
Z42.1 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Type 1 Excludes
- deformity and disproportion of reconstructed breast N65.1
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
- Admission (for) - See Also: Encounter (for);
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Admission(for)
- breast reconstruction following mastectomy
- Encounter(with health service) (for)
- breast reconstruction following mastectomy
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Breast Reconstruction
If you need a mastectomy, you have a choice about whether or not to have surgery to rebuild the shape of the breast. Instead of breast reconstruction, you could choose to wear a breast form that replaces the breast, wear padding inside your bra, or do nothing. All of these options have pros and cons.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert Z42.1 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About Z42.1Overview
Is Z42.1 a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report encounter for breast reconstruction following mastectomy on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does Z42.1 group to?
When encounter for breast reconstruction following mastectomy is the principal diagnosis on an inpatient stay, it groups to MS-DRG 606, 607, with relative weights from 0.9064 to 1.5132 depending on complications. Higher weights mean higher Medicare reimbursement.
Who can Z42.1 be reported for?
The Medicare Code Editor checks encounter for breast reconstruction following mastectomy against patient demographics: this code is intended for adult patients (age 15 through 124). Claims outside these limits are flagged as inconsistent.
Is Z42.1 exempt from POA reporting?
Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for encounter for breast reconstruction following mastectomy on inpatient claims.
What is the ICD-9 equivalent of Z42.1?
Under the General Equivalence Mappings, encounter for breast reconstruction following mastectomy converts to ICD-9-CM V51.0 (brst reconst fol mastect). The mapping is a direct match.
