Question 1

What is ICD-10 code A99?

Accepted Answer

A99 is the ICD-10-CM diagnosis code for unspecified viral hemorrhagic fever. A serious viral infection that causes bleeding and is not identified as a specific type of hemorrhagic fever virus. A99 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering arthropod-borne viral fevers and viral hemorrhagic fevers (a90-a99).

A99 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 only when the specific viral hemorrhagic fever cannot be determined.

Question 2

Is A99 an HCC code?

Accepted Answer

No. A99 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 A99 billable?

Accepted Answer

Yes. A99 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. A99 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 A99?

Accepted Answer

A99 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 A99 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 A99?

Accepted Answer

Use this code only when the specific viral hemorrhagic fever cannot be determined Consider requesting additional testing or clinical documentation to identify the specific virus if possible

HCC Buddy Code Card

A99

Is A99 an HCC code?

What This Code Means

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Work A99 in HCC Buddy

A99 ICD-10-CM Code: Unspecified viral hemorrhagic fever

HCC Buddy Code Card

A99

Is A99 an HCC code?

What This Code Means

Coding Tips

Code Hierarchy

Work A99 in HCC Buddy