Question 1

What is ICD-10 code M85.00?

Accepted Answer

M85.00 is the ICD-10-CM diagnosis code for fibrous dysplasia (monostotic), unspecified site. Fibrous dysplasia is a condition where normal bone is replaced by fibrous tissue, affecting a single bone at an unspecified location. M85.00 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering disorders of bone density and structure (m80-m85).

M85.00 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.

Fibrous dysplasia (monostotic) affects only one bone; if multiple bones are involved, use polyostotic codes instead.

Question 2

Is M85.00 an HCC code?

Accepted Answer

No. M85.00 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 M85.00 billable?

Accepted Answer

Yes. M85.00 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. M85.00 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 M85.00?

Accepted Answer

M85.00 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 M85.00 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 M85.00?

Accepted Answer

Fibrous dysplasia (monostotic) affects only one bone; if multiple bones are involved, use polyostotic codes instead Specify the anatomical site when possible rather than using the unspecified code

M85.00

Is M85.00 an HCC code?

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Open M85.00 in the Interactive Encoder