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C4A.71 ICD-10-CM Code: Merkel cell carcinoma of right lower limb, including hip

C4A.71 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 · HCC coding software

ICD-10-CM Code View

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Code lookupC4A.71

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

C4A.71

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

Merkel cell carcinoma of right lower limb, including hip

Merkel cell carcinoma is a rare and aggressive skin cancer that develops from neuroendocrine cells in the skin. This code specifically identifies the cancer when it occurs on the right lower limb, including the hip area.

Buddy the Bee presenting code insight

Buddy Insight

Merkel cell carcinoma of the right lower limb, including hip is a rare aggressive neuroendocrine cutaneous malignancy.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 21

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

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 012

Code-level coefficient reference

ESRD/PACE

HCC 12

Code-level coefficient reference

RXHCC

HCC 22

Code-level coefficient reference

Code Book Path

Official
C4AMerkel cell carcinomaC4A.7Merkel cell carcinoma of lower limb, including hipC4A.71Merkel cell carcinoma of right lower limb, including hip

Inclusion Terms

Official

No inclusion terms are included in this display for C4A.71. Check the code and parent instructions in the Code Book.

Excludes 2

Official

No Excludes 2 notes are included in this display for C4A.71. Check the code and parent instructions in the Code Book.

Related Codes

Official
C4A.70Merkel cell carcinoma of unspecified lower limb, including hipC4A.72Merkel cell carcinoma of left lower limb, including hip

Includes

Official

No Includes notes are included in this display for C4A.71. Check the code and parent instructions in the Code Book.

Excludes 1

Official

No Excludes 1 notes are included in this display for C4A.71. 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.71. 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.71. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C4A.71. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Histopathologic confirmation of Merkel cell carcinoma with immunohistochemistry
Laterality documented as right
Specific lower limb subsite (hip, thigh, knee, lower leg, ankle, foot, toes)
Tumor dimensions and depth of invasion

MEAT Support

HCC Buddy guidance
Histopathologic confirmation of Merkel cell carcinoma with immunohistochemistry
Laterality documented as right
Specific lower limb subsite (hip, thigh, knee, lower leg, ankle, foot, toes)
Tumor dimensions and depth of invasion

Audit Caution

HCC Buddy guidance
Confusing right vs. left lower limb laterality — always verify from surgical or pathology documentation
Using C44 lower limb skin cancer codes instead of C4A for Merkel cell carcinoma
Assigning hip lesions to trunk codes (C4A.59) when hip is included in lower limb codes
Not distinguishing Merkel cell carcinoma from other cutaneous malignancies — histopathology confirmation is essential

Common Mistakes

HCC Buddy guidance
C4A.72 — Merkel cell carcinoma of left lower limb; laterality reversed
C4A.70 — Merkel cell carcinoma of unspecified lower limb; use only when laterality is undocumented
C44.711 — Other malignant neoplasm of right lower limb skin; for non-Merkel cell skin cancers
C43.71 — Melanoma of right lower limb including hip; different histology

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.71 an HCC code?

Yes. C4A.71 (Merkel cell carcinoma of right lower limb, including hip) 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.71 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.71
Description
Merkel cell carcinoma of right lower limb, including hip
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.71 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C4A.71

For C4A.71, 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.71 is the ICD-10-CM diagnosis code for merkel cell carcinoma of right lower limb, including hip. Merkel cell carcinoma is a rare and aggressive skin cancer that develops from neuroendocrine cells in the skin. This code specifically identifies the cancer when it occurs on the right lower limb, including the hip area. C4A.71 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.71 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.

Verify laterality (right vs. left) is clearly documented in the medical record before assigning this code, as the 7th character specifies right lower limb. For C4A.71, 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.71 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Verify laterality (right vs. left) is clearly documented in the medical record before assigning this code, as the 7th character specifies right lower limb
  • •Merkel cell carcinoma requires a 7th character for laterality; ensure you use the complete code with the appropriate character to indicate the specific anatomical location

Clinical Significance

Merkel cell carcinoma of the right lower limb, including hip is a rare aggressive neuroendocrine cutaneous malignancy. Lower extremity lesions drain to inguinal and pelvic lymph nodes, making inguinal sentinel lymph node biopsy essential for staging. Lower limb Merkel cell carcinoma may present at a larger size than head/neck lesions due to delayed detection in areas often covered by clothing.

Documentation Requirements

  • ✓Histopathologic confirmation of Merkel cell carcinoma with immunohistochemistry
  • ✓Laterality documented as right
  • ✓Specific lower limb subsite (hip, thigh, knee, lower leg, ankle, foot, toes)
  • ✓Tumor dimensions and depth of invasion
  • ✓Inguinal sentinel lymph node biopsy status and results
  • ✓Staging per American Joint Committee on Cancer criteria
  • ✓Treatment plan documentation

Commonly Confused Codes

  • •C4A.72: Merkel cell carcinoma of left lower limb; laterality reversed
  • •C4A.70: Merkel cell carcinoma of unspecified lower limb; use only when laterality is undocumented
  • •C44.711: Other malignant neoplasm of right lower limb skin; for non-Merkel cell skin cancers
  • •C43.71: Melanoma of right lower limb including hip; different histology
  • •C4A.59: Merkel cell carcinoma of other trunk; hip area boundary can be ambiguous

Child Codes

C4A.70Merkel cell carcinoma of unspecified lower limb, including hip
HCC 21
C4A.71Merkel cell carcinoma of right lower limb, including hip
HCC 21
C4A.72Merkel cell carcinoma of left lower limb, including hip
HCC 21

Code Hierarchy

└C4AMerkel cell carcinoma└C4A.7Merkel cell carcinoma of lower limb, including hip└C4A.71Merkel cell carcinoma of right lower limb, including hip
└C4A.71Merkel cell carcinoma of right lower limb, including hip

Also searched as

  • C4A 71
  • C4A71

For C4A.71, 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.

C4A.71 maps to CMS-HCC V28 category 21, Lymphoma and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C4A.71. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

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