Question 1

What is ICD-10 code M61.521?

Accepted Answer

M61.521 is the ICD-10-CM diagnosis code for other ossification of muscle, right upper arm. Abnormal bone-like tissue forming in the muscles of the right upper arm, causing hardening and potential loss of arm function. M61.521 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering disorders of muscles (m60-m63).

M61.521 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 'right' laterality is documented; distinguish between upper arm (shoulder to elbow) and forearm.

Question 2

Is M61.521 an HCC code?

Accepted Answer

No. M61.521 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 M61.521 billable?

Accepted Answer

Yes. M61.521 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. M61.521 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 M61.521?

Accepted Answer

M61.521 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 M61.521 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 M61.521?

Accepted Answer

Confirm 'right' laterality is documented; distinguish between upper arm (shoulder to elbow) and forearm Often associated with brachial artery injury or severe trauma; review clinical history

M61.521

Is M61.521 an HCC code?

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Open M61.521 in the Interactive Encoder