Question 1

What is ICD-10 code M13.879?

Accepted Answer

M13.879 is the ICD-10-CM diagnosis code for other specified arthritis, unspecified ankle and foot. A type of arthritis affecting the ankle and foot that doesn't fit into other specific arthritis categories, when the side is not specified. M13.879 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering inflammatory polyarthropathies (m05-m14).

M13.879 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.

Only use when documentation does not specify right or left; query provider if laterality can be determined.

Question 2

Is M13.879 an HCC code?

Accepted Answer

No. M13.879 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 M13.879 billable?

Accepted Answer

Yes. M13.879 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. M13.879 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 M13.879?

Accepted Answer

M13.879 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 M13.879 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 M13.879?

Accepted Answer

Only use when documentation does not specify right or left; query provider if laterality can be determined This is a less specific code; prefer M13.871 or M13.872 when side is documented

M13.879

Is M13.879 an HCC code?

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