Question 1

What is ICD-10 code Z23?

Accepted Answer

Z23 is the ICD-10-CM diagnosis code for encounter for immunization. A visit to receive a vaccination or immunization to prevent disease. Z23 sits in the ICD-10-CM chapter for factors influencing health status and contact with health services (z00-z99), within the section covering persons with potential health hazards related to communicable diseases (z20-z29).

Z23 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

Always include the specific vaccine code(s) administered in addition to Z23.

Question 2

Is Z23 an HCC code?

Accepted Answer

No. Z23 is a billable ICD-10-CM code but does not map to any payment HCC category under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can still be reported on Medicare Advantage encounter data submissions, but it does not contribute to the beneficiary's Risk Adjustment Factor (RAF) score and therefore does not affect the risk-adjusted capitation payment to the plan. V28 reached 100% phase-in for payment year 2026.

Question 3

Is Z23 billable?

Accepted Answer

Yes. Z23 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. Z23 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Question 4

What is the V28 vs V24 difference for Z23?

Accepted Answer

Z23 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither model rewards Z23 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a payment HCC.

Question 5

What should coders know when reporting Z23?

Accepted Answer

Always include the specific vaccine code(s) administered in addition to Z23 This code is used for preventive visits and should be paired with procedure codes for the actual vaccination

HCC Buddy Code Card

Z23

Is Z23 an HCC code?

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Open Z23 in the Interactive Encoder

Z23 ICD-10-CM Code: Encounter for immunization

HCC Buddy Code Card

Z23

Is Z23 an HCC code?

What This Code Means

Coding Tips

Code First

Code Also

Code Hierarchy

Open Z23 in the Interactive Encoder