Question 1

What is ICD-10 code D05.91?

Accepted Answer

D05.91 is the ICD-10-CM diagnosis code for unspecified type of carcinoma in situ of right breast. Pre-cancerous breast cell abnormalities in the right breast that have not spread beyond the breast tissue, but the specific type is not documented. D05.91 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering in situ neoplasms (d00-d09).

D05.91 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 laterality is documented as right breast but the specific type of carcinoma in situ is not specified.

Question 2

Is D05.91 an HCC code?

Accepted Answer

No. D05.91 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 D05.91 billable?

Accepted Answer

Yes. D05.91 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. D05.91 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 D05.91?

Accepted Answer

D05.91 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 D05.91 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 D05.91?

Accepted Answer

Use this code when laterality is documented as right breast but the specific type of carcinoma in situ is not specified Query the provider to determine if the condition is lobular, intraductal, or another specified type

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D05.91

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D05.91 ICD-10-CM Code: Unspecified type of carcinoma in situ of right breast

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D05.91

Is D05.91 an HCC code?

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