2027 ICD-10-CM Diagnosis Code Z42.1Encounter for breast reconstruction following mastectomy

ICD-10-CM Codes›Z00–Z99›Z40-Z53›Z42

ICD-10-CM Z42.1
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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 2027 (October 1, 2026 through September 30, 2027) 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

ICD-10-CM Code
Z42.1
Billable Status
Yes — Valid for Submission
Code Describes
Encounter for breast reconstruction following mastectomy
Short Description
Encounter for breast reconstruction following mastectomy
Same as the full description in the CMS dataset.
Parent Code
Z42
Encounter for plastic and reconstructive surgery following medical procedure or healed injury

Code Classification

ChapterZ00–Z99Factors influencing health status and contact with health services
SectionZ40-Z53Encounters for other specific health care
CategoryZ42Encounter for plastic and reconstructive surgery following medical procedure or healed injury
This CodeZ42.1Encounter for breast reconstruction following mastectomy

Code EditsBilling

Medicare Code Editor checks that affect claim validity for Z42.1.

Adult diagnoses
The Medicare Code Editor detects inconsistencies in adult cases by checking a patient's age and any diagnosis on the patient's record. The adult code edits apply to patients age range is 15–124 years inclusive (e.g., senile delirium, mature cataract).

Present on Admission (POA)Billing

Z42.1 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Encounters for other specific health care (Z40-Z53).

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Z42.1: its own notes plus those printed at Z42, block Z40-Z53, and Chapter 21. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

On Z42.1 itself
  • deformity and disproportion of reconstructed breast (N65.1-)
From Z42 Encounter for plastic and reconstructive surgery following medical procedure or healed injury applies to 2 codes
  • encounter for cosmetic plastic surgery (Z41.1)
  • encounter for plastic surgery for treatment of current injury - code to relevent injury

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.

From Block Z40-Z53 Encounters for other specific health care applies to 164 codes
  • follow-up examination for medical surveillance after treatment (Z08-Z09)

Notes

General instructions on how these codes are used.

From Chapter 21 (Z00-Z99) Factors influencing health status and contact with health services applies to 1,425 codes
  • Z codes represent reasons for encounters. A corresponding procedure code must accompany a Z code if a procedure is performed. Categories Z00-Z99 are provided for occasions when circumstances other than a disease, injury or external cause classifiable to categories A00-Y89 are recorded as 'diagnoses' or 'problems'. This can arise in two main ways:
  • (a) When a person who may or may not be sick encounters the health services for some specific purpose, such as to receive limited care or service for a current condition, to donate an organ or tissue, to receive prophylactic vaccination (immunization), or to discuss a problem which is in itself not a disease or injury.
  • (b) When some circumstance or problem is present which influences the person's health status but is not in itself a current illness or injury.

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Z42.1, its category, or a range that includes it.

Excludes1 4

These codes carry an Excludes1 note naming Z42.1: they are not reported together with it, unless the two conditions are unrelated.

  • Z41.1 Encounter for cosmetic surgery
    encounter for post-mastectomy breast implantation (Z42.1)
  • Z44.3 Encounter for fitting and adjustment of external breast prosthesis
    encounter for breast reconstruction following mastectomy (Z42.1)
  • Z45.81 Encounter for adjustment or removal of breast implant
    encounter for breast reconstruction following mastectomy (Z42.1)
  • Z41.1 Encounter for cosmetic surgery
    encounter for plastic and reconstructive surgery following medical procedure or healed injury (Z42.-) names Z42.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR FAC004
Encounter for prophylactic or other procedures
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

ICD-9-CM
V51.0 Brst reconst fol mastect
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Z42.1Overview

What is the ICD-10 code for encounter for breast reconstruction following mastectomy?

The ICD-10-CM code for encounter for breast reconstruction following mastectomy is Z42.1 (sometimes written as Z421). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 607, 606, with relative weights from 0.8772 to 1.5721 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. The code appears in the Encounters for other specific health care (Z40-Z53) range of the CMS exempt list.