Z23 Encounter for immunization

The ICD-10-CM code for Encounter for immunization is Z23 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

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

Section

Z20-Z29: Persons with potential health hazards related to communicable diseases (Z20-Z29)

Category Z23

1 code (1 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to Z23:

• Prophylactic › vaccination
• Immunization › encounter for
• Vaccination (prophylactic) › encounter for
• Admission (for) › prophylactic (measure) › vaccination

U.S. Hospital Utilization

• An estimated 2,940,651 U.S. inpatient stays in 2023 included Z23 among the documented diagnoses.
• 780 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

Inoculations and vaccinations (Z23) with procedure code requirement

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.

Used with any code in range A00.0-T88.9, Z00-Z99

1) Used with any code in the range of A00.0-T88.9, Z00-Z99 An external cause code may be used with any code in the range of A00.0-T88.9, Z00-Z99, classification that represents a health condition due to an external cause. Though they are most applicable to injuries, they are also valid for use with such things as infections or diseases due to an external source, and other health conditions, such as a heart attack that occurs during strenuous physical activity.

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)