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Z23 ICD-10-CM Code: Encounter for immunization

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
1 code-first instruction · 1 code-also instruction

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 795 — NORMAL NEWBORN (MDC 15)
  • MS-DRG 951 — OTHER FACTORS INFLUENCING HEALTH STATUS (MDC 23)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for Z23 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Code First

Underlying conditions that must be sequenced before this code.

  • any routine childhood examination

Code Also

Additional codes that may be required to fully describe the encounter.

  • Code also, if applicable, encounter for immunization safety counseling (Z71.85)

Coder workflow for Z23

MedCoder structured workflow — derived from this code’s own official record

Before you code Z23

  1. Confirm the reason for the encounter this Z code records: the circumstance it records. Check whether the code may be reported as first-listed or principal — some Z codes are limited to one position — and do not report a history or status code for a condition documented as current. Z code categories and their reporting positions (Guidelines I.C.21.c, I.C.21.c.15).

    Guide: Z codes as principal or first-listed diagnosis →

Choose the right path

  1. Is the underlying (etiologic) condition the Code First note names documented?
    Yes → Sequence the underlying condition first, then Z23.
    No → Continue; do not add an underlying condition the record does not document.

Consider Z23. Then review the Code Also note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
The underlying (etiologic) condition
Named in the Code First note; sequenced before this code when documented (Guidelines I.A.13).
The reason for the encounter
Whether the code records the encounter’s purpose, a status, or a history — and whether it may be first-listed (Guidelines I.C.21.c).

Official instructions as workflow

  • Code First — sequencing check(1 note)

    Coding workflow: Check whether the underlying or etiologic condition the note names is documented. When it is, sequence it before Z23. Do not add an underlying condition the record does not document.

    See the official tabular notes · Guidelines I.A.13

  • Code Also — related condition(1 note)

    Coding workflow: Review the related condition when both are documented and the instruction applies. A Code Also note does not fix sequencing; the order follows the circumstances of the encounter.

    ReviewZ71.85

    See the official tabular notes · Guidelines I.A.17

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The underlying condition the Code First note names is documented alongside this condition.

Coding question: How are the two sequenced?

Path: Review the Code First note.

Reason: The underlying condition is sequenced first and the manifestation follows (Guidelines I.A.13).

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Encounter for immunization is a billable ICD-10-CM diagnosis code (Z23).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (4)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Chapter 21: Factors influencing health status and contact with health services (Z00-Z99)

2) Inoculations and vaccinations Code Z23 is for encounters for inoculations and vaccinations. It indicates that a patient is being seen to receive a prophylactic inoculation against a disease. Procedure codes are required to identify the actual administration of the injection and the type(s) of immunizations given. Code Z23 may be used as a secondary code if the inoculation is given as a routine part of preventive health care, such as a well-baby visit.

Verify Before Coding

  • Principal-diagnosis restriction. The Medicare Code Editor lists this code as unacceptable as a principal diagnosis: it describes a circumstance influencing health status rather than a current illness or injury being treated. It is valid as a secondary diagnosis.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name Z23 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 2 Code Also instructions: Z71.84 — Encounter for health counseling related to travel, Z71.85 — Encounter for immunization safety counseling.

These codes suggest coding this condition alongside when both are present.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 2 MS-DRGs: DRG 795 (MDC 15), DRG 951 (MDC 23).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):FAC016 — Exposure, encounters, screening or contact with infectious disease (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Principal diagnosis restriction (Medicare Code Editor)

Not acceptable as a principal diagnosis on an inpatient claim.

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Exposure, encounters, screening or contact with infectious disease).

Z11.8 — Encounter for screening for other infectious and parasitic diseases, Z11.9 — Encounter for screening for infectious and parasitic diseases, unspecified, Z20.01 — Contact with and (suspected) exposure to intestinal infectious diseases due to Escherichia coli (E. coli), Z20.09 — Contact with and (suspected) exposure to other intestinal infectious diseases, Z20.1 — Contact with and (suspected) exposure to tuberculosis, Z20.2 — Contact with and (suspected) exposure to infections with a predominantly sexual mode of transmission, Z20.3 — Contact with and (suspected) exposure to rabies, Z20.4 — Contact with and (suspected) exposure to rubella, Z20.5 — Contact with and (suspected) exposure to viral hepatitis, Z20.6 — Contact with and (suspected) exposure to human immunodeficiency virus [HIV], Z20.7 — Contact with and (suspected) exposure to pediculosis, acariasis and other infestations, Z20.810 — Contact with and (suspected) exposure to anthrax, Z20.811 — Contact with and (suspected) exposure to meningococcus, Z20.818 — Contact with and (suspected) exposure to other bacterial communicable diseases, Z20.820 — Contact with and (suspected) exposure to varicella, Z20.821 — Contact with and (suspected) exposure to Zika virus, Z20.822 — Contact with and (suspected) exposure to COVID-19, Z20.828 — Contact with and (suspected) exposure to other viral communicable diseases, Z20.89 — Contact with and (suspected) exposure to other communicable diseases, Z20.9 — Contact with and (suspected) exposure to unspecified communicable disease, +15 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Immunization”, “Vaccination”, “Admission”; these codes share that main term but sit in a different category of the Tabular List.

Z01.021 — Encounter for examination of eyes and vision following failed vision screening with abnormal findings (vision examination, following failed vision screening, with abnormal findings), Z01.10 — Encounter for examination of ears and hearing without abnormal findings (examination at health care facility, ear), Z01.118 — Encounter for examination of ears and hearing with other abnormal findings (examination at health care facility, ear, with abnormal findings NEC), Z01.20 — Encounter for dental examination and cleaning without abnormal findings (examination at health care facility, dental), Z01.21 — Encounter for dental examination and cleaning with abnormal findings (examination at health care facility, dental, with abnormal findings), Z01.82 — Encounter for allergy testing (sensitivity test, allergy NEC), Z04.6 — Encounter for general psychiatric examination, requested by authority (psychiatric examination, requested by authority), Z09 — Encounter for follow-up examination after completed treatment for conditions other than malignant neoplasm (follow-up examination), Z11.1 — Encounter for screening for respiratory tuberculosis (sensitivity test, Mantoux), Z12.4 — Encounter for screening for malignant neoplasm of cervix (Papanicolaou smear, cervix), Z28.01 — Immunization not carried out because of acute illness of patient (not done, because, acute illness of patient), Z28.02 — Immunization not carried out because of chronic illness or condition of patient (not done, because, chronic illness of patient), Z28.03 — Immunization not carried out because of immune compromised state of patient (not done, because, immune compromised state of patient), Z28.04 — Immunization not carried out because of patient allergy to vaccine or component (not done, because, allergy to vaccine), Z28.09 — Immunization not carried out because of other contraindication (not done, because, contraindication NEC), Z28.1 — Immunization not carried out because of patient decision for reasons of belief or group pressure (not done, because, group pressure), Z28.20 — Immunization not carried out because of patient decision for unspecified reason (not done, because, unspecified patient reason), Z28.21 — Immunization not carried out because of patient refusal (not done, because, patient refusal), Z28.29 — Immunization not carried out because of patient decision for other reason (not done, because, specified reason NEC, of patient), Z28.311 — Partially vaccinated for COVID-19 (partial, for COVID-19), +103 more

Contextual Map

Every relationship of Z23 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run Z23 with these 2 related codes in Claim Check

Hierarchy

Code Also

Referenced by Code Also instructions

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

Index entries

  • Admission (for), prophylactic (measure), vaccination[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Immunization, encounter for[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Prophylactic, vaccination[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Vaccination (prophylactic), encounter for[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Common coding questions

Is Z23 the only diagnosis needed for a flu shot visit?

For an encounter that is only the immunization, Z23 is the diagnosis code — one code for all vaccine types — the tabular’s own note says procedure codes identify the immunizations given. When the shot happens during a routine childhood examination, Z23’s Code First note puts the examination code first. See When can a Z code be the primary diagnosis?.

What does Z23 pair with when counseling happens?

Its Code Also note names Z71.85, encounter for immunization safety counseling, when applicable — the counseling gets its own code beside Z23 rather than replacing it.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Coding guidelines Official source data
ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "Z23 — Encounter for immunization." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/z23-encounter-for-immunization

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Encounter for immunization

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027 (effective October 1, 2026), and none are recorded for this code. Note changes are tracked from FY2027 only.