Question 1

What is ICD-10 code G56.21?

Accepted Answer

G56.21 is the ICD-10-CM diagnosis code for lesion of ulnar nerve, right upper limb. Damage or injury to the ulnar nerve in the right arm, causing weakness or numbness in the hand and pinky side of the palm. G56.21 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering nerve, nerve root and plexus disorders (g50-g59).

G56.21 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 side laterality is explicitly documented before assigning this code.

Question 2

Is G56.21 an HCC code?

Accepted Answer

No. G56.21 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 G56.21 billable?

Accepted Answer

Yes. G56.21 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. G56.21 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

Which HCC does G56.21 map to under V28?

Accepted Answer

G56.21 does not map to a CMS-HCC V28 payment category. Check the current CMS-HCC V28 model file for payment year 2026 rather than an older V24 tip sheet.

Question 5

What does G56.21 pay in RAF?

Accepted Answer

G56.21 has no separately stated V28 community RAF weight. If it is not a V28 payment HCC, it adds nothing to a community RAF score.

Question 6

What is the V28 vs V24 difference for G56.21?

Accepted Answer

G56.21 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 community model rewards G56.21 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's V28/V24 community RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a community payment HCC.

Question 7

What documentation supports G56.21?

Accepted Answer

Confirm right side laterality is explicitly documented before assigning this code Document the etiology (compression, trauma, etc.) if available for clinical clarity G56.21 is not a CMS-HCC payment code, so MEAT is not the payment hook. Documentation still has to support the diagnosis if you report it.

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G56.21

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G56.21 ICD-10-CM Code: Lesion of ulnar nerve, right upper limb

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G56.21

Is G56.21 an HCC code?

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