Question 1

What is ICD-10 code B04?

Accepted Answer

B04 is the ICD-10-CM diagnosis code for monkeypox. Monkeypox, a viral infection similar to smallpox but typically milder, transmitted from animals to humans or between humans. B04 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering viral infections characterized by skin and mucous membrane lesions (b00-b09).

B04 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.

Confirm laboratory confirmation of monkeypox diagnosis before coding, as clinical presentation can mimic other conditions.

Question 2

Is B04 an HCC code?

Accepted Answer

No. B04 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 B04 billable?

Accepted Answer

Yes. B04 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. B04 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 B04?

Accepted Answer

B04 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 B04 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 B04?

Accepted Answer

Confirm laboratory confirmation of monkeypox diagnosis before coding, as clinical presentation can mimic other conditions Report confirmed cases to public health authorities as required by law

B04

Is B04 an HCC code?

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Open B04 in the Interactive Encoder