Question 1

What is ICD-10 code M65.921?

Accepted Answer

M65.921 is the ICD-10-CM diagnosis code for unspecified synovitis and tenosynovitis, right upper arm. Inflammation of the tissue lining tendons and joints in the right upper arm. This causes pain, swelling, and weakness in the arm muscles and surrounding tissues. M65.921 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering disorders of synovium and tendon (m65-m67).

M65.921 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 documentation specifies 'right' upper arm to ensure accurate laterality coding.

Question 2

Is M65.921 an HCC code?

Accepted Answer

No. M65.921 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 M65.921 billable?

Accepted Answer

Yes. M65.921 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. M65.921 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 M65.921?

Accepted Answer

M65.921 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 M65.921 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 M65.921?

Accepted Answer

Confirm documentation specifies 'right' upper arm to ensure accurate laterality coding Distinguish between upper arm involvement and shoulder or forearm involvement for proper code selection

M65.921

Is M65.921 an HCC code?

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Open M65.921 in the Interactive Encoder