Question 1

What is ICD-10 code A18.81?

Accepted Answer

A18.81 is the ICD-10-CM diagnosis code for tuberculosis of thyroid gland. This is a tuberculosis infection that has spread to the thyroid gland, the butterfly-shaped gland in the neck that controls metabolism. It is a rare form of extrapulmonary tuberculosis where the TB bacteria infect thyroid tissue. A18.81 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering tuberculosis (a15-a19).

A18.81 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.

This code is part of the tuberculosis chapter (A15-A19) and should only be used when TB of the thyroid is confirmed, not suspected; verify documentation confirms tuberculosis involvement of the thyroid specifically.

Question 2

Is A18.81 an HCC code?

Accepted Answer

No. A18.81 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 A18.81 billable?

Accepted Answer

Yes. A18.81 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. A18.81 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

Which HCC does A18.81 map to under V28?

Accepted Answer

A18.81 does not map to a CMS-HCC V28 payment category. Check the current CMS-HCC V28 model file for payment year 2026 rather than an older V24 tip sheet.

Question 5

What does A18.81 pay in RAF?

Accepted Answer

A18.81 has no separately stated V28 community RAF weight. If it is not a V28 payment HCC, it adds nothing to a community RAF score.

Question 6

What is the V28 vs V24 difference for A18.81?

Accepted Answer

A18.81 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 community model rewards A18.81 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's V28/V24 community RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a community payment HCC.

Question 7

What documentation supports A18.81?

Accepted Answer

This code is part of the tuberculosis chapter (A15-A19) and should only be used when TB of the thyroid is confirmed, not suspected; verify documentation confirms tuberculosis involvement of the thyroid specifically This is a manifestation code that may require an additional code to identify the type of TB (such as drug-resistant TB) if applicable; always check for any associated pulmonary TB or other organ involvement that should be coded separately A18.81 is not a CMS-HCC payment code, so MEAT is not the payment hook. Documentation still has to support the diagnosis if you report it.

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A18.81

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A18.81 ICD-10-CM Code: Tuberculosis of thyroid gland

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A18.81

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