C4A.30 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

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Code lookupC4A.30

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Melanoma and other malignant neoplasms of skin (C43-C44)

C4A.30

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Merkel cell carcinoma of unspecified part of face

A rare aggressive skin cancer (Merkel cell carcinoma) that develops somewhere on the face, but the specific facial location is not specified.

Buddy Insight

Merkel cell carcinoma of unspecified part of face represents a rare neuroendocrine skin malignancy in a high-visibility anatomical region.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 21

Lymphoma and Other Cancers

Coefficient HCC 21: 0.671 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 012

HHS-HCC 012 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 12

Breast/Prostate/and Other Can...

Code-level coefficient reference

RXHCC

Mapped

HCC 22

Prostate, Breast, Bladder, an...

Code-level coefficient reference

Code Book Path

Official

C4AMerkel cell carcinoma C4A.3Merkel cell carcinoma of other and unspecified parts of face C4A.30Merkel cell carcinoma of unspecified part of face

Inclusion Terms

Official

No inclusion terms are included in this display for C4A.30. Check the code and parent instructions in the Code Book.

Excludes 2

Official

No Excludes 2 notes are included in this display for C4A.30. Check the code and parent instructions in the Code Book.

Related Codes

Official

C4A.31Merkel cell carcinoma of nose C4A.39Merkel cell carcinoma of other parts of face

Includes

Official

No Includes notes are included in this display for C4A.30. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for C4A.30. Check the code and parent instructions in the Code Book.

Code First

Official

No Code First sequencing instructions are included in this display for C4A.30. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C4A.30. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C4A.30. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Histopathologic confirmation of Merkel cell carcinoma (CK20+, TTF-1 negative on immunohistochemistry)

Specific facial location should be queried — nose, lip, cheek, forehead, chin, temple

Tumor size and depth of invasion

Regional lymph node status (cervical, submandibular, parotid nodes)

MEAT Support

HCC Buddy guidance

Histopathologic confirmation of Merkel cell carcinoma (CK20+, TTF-1 negative on immunohistochemistry)

Specific facial location should be queried — nose, lip, cheek, forehead, chin, temple

Tumor size and depth of invasion

Regional lymph node status (cervical, submandibular, parotid nodes)

Audit Caution

HCC Buddy guidance

Using this unspecified code when a more specific facial subsite is documented — always check for nose (C4A.31) or other face (C4A.39)

Confusing C4A face codes with C44 face codes — Merkel cell carcinoma requires C4A specifically

Failing to query the provider for specific facial location before defaulting to unspecified

Not coding associated metastatic disease separately when present

Common Mistakes

HCC Buddy guidance

C4A.31 — Merkel cell carcinoma of nose; use this more specific code when nasal location is documented

C4A.39 — Merkel cell carcinoma of other parts of face; use when a specific non-nose facial site is documented

C44.30x — Other malignant skin neoplasm of unspecified face; not Merkel cell — different subcategory

C43.30 — Melanoma of unspecified part of face; different histology entirely

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C4A.30 an HCC code?

Yes. C4A.30 (Merkel cell carcinoma of unspecified part of face) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C4A.30 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C4A.30
Description: Merkel cell carcinoma of unspecified part of face
HCC (V28): HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient: 0.671
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers

0.671

ESRDHCC 12, Breast/Prostate/and Other Cancers and Tumors

Not separately weighted

RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C4A.30 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C4A.30

For C4A.30, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Coder workflow notes

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What This Code Means

C4A.30 is the ICD-10-CM diagnosis code for merkel cell carcinoma of unspecified part of face. A rare aggressive skin cancer (Merkel cell carcinoma) that develops somewhere on the face, but the specific facial location is not specified. C4A.30 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering melanoma and other malignant neoplasms of skin (c43-c44).

Under the CMS-HCC V28 risk adjustment model, C4A.30 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Use this code only when the specific facial location is not documented; if a specific site like nose is documented, use C4A.31 or other more specific codes. For C4A.30, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for C4A.30 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use this code only when the specific facial location is not documented; if a specific site like nose is documented, use C4A.31 or other more specific codes
•This is a less specific code; attempt to obtain more detailed anatomical documentation when possible

Clinical Significance

Merkel cell carcinoma of unspecified part of face represents a rare neuroendocrine skin malignancy in a high-visibility anatomical region. Facial Merkel cell carcinoma is particularly concerning due to proximity to critical structures and rich lymphatic drainage of the head and neck. This unspecified code indicates documentation does not identify the precise facial subsite.

Documentation Requirements

✓Histopathologic confirmation of Merkel cell carcinoma (CK20+, TTF-1 negative on immunohistochemistry)
✓Specific facial location should be queried — nose, lip, cheek, forehead, chin, temple
✓Tumor size and depth of invasion
✓Regional lymph node status (cervical, submandibular, parotid nodes)
✓Surgical margin status if excision performed
✓Treatment modality and current disease status

Commonly Confused Codes

•C4A.31: Merkel cell carcinoma of nose; use this more specific code when nasal location is documented
•C4A.39: Merkel cell carcinoma of other parts of face; use when a specific non-nose facial site is documented
•C44.30x: Other malignant skin neoplasm of unspecified face; not Merkel cell: different subcategory
•C43.30: Melanoma of unspecified part of face; different histology entirely