Question 1

What is ICD-10 code Z16.31?

Accepted Answer

Z16.31 is the ICD-10-CM diagnosis code for resistance to antiparasitic drug(s). A condition where parasites (organisms that live on or in the body) have become resistant to medications designed to kill them, making treatment more difficult. Z16.31 sits in the ICD-10-CM chapter for factors influencing health status and contact with health services (z00-z99), within the section covering resistance to antimicrobial drugs (z16).

Z16.31 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.

Use this code when documentation confirms parasitic infection with documented resistance to antiparasitic agents.

Question 2

Is Z16.31 an HCC code?

Accepted Answer

No. Z16.31 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 Z16.31 billable?

Accepted Answer

Yes. Z16.31 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. Z16.31 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 Z16.31?

Accepted Answer

Z16.31 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 Z16.31 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 Z16.31?

Accepted Answer

Use this code when documentation confirms parasitic infection with documented resistance to antiparasitic agents This is a Z code (status/history code) and should be used as a secondary diagnosis with the primary parasitic infection code

HCC Buddy Code Card

Z16.31

Is Z16.31 an HCC code?

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Open Z16.31 in the Interactive Encoder

Z16.31 ICD-10-CM Code: Resistance to antiparasitic drug(s)

HCC Buddy Code Card

Z16.31

Is Z16.31 an HCC code?

What This Code Means

Coding Tips

Child Codes

Code Hierarchy

Open Z16.31 in the Interactive Encoder