Question 1

What is ICD-10 code M85.042?

Accepted Answer

M85.042 is the ICD-10-CM diagnosis code for fibrous dysplasia (monostotic), left hand. A benign bone condition where fibrous tissue abnormally grows in the left hand bone, causing the bone structure to weaken and potentially affect hand function. M85.042 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).

M85.042 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.

Verify laterality is documented as 'left' in the medical record before assigning this code.

Question 2

Is M85.042 an HCC code?

Accepted Answer

No. M85.042 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 M85.042 billable?

Accepted Answer

Yes. M85.042 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. M85.042 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 M85.042?

Accepted Answer

M85.042 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 M85.042 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 M85.042?

Accepted Answer

Verify laterality is documented as 'left' in the medical record before assigning this code This code applies to any bone in the left hand, including metacarpals and phalanges

M85.042

Is M85.042 an HCC code?

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