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C40.91 ICD-10-CM Code: Malignant neoplasm of unspecified bones and articular cartilage of right limb

C40.91 maps to CMS-HCC V28 21 (RAF 0.671). Documentation must support MEAT. MEAT criteria · RAF calculator · HCC coding software

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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of bone and articular cartilage (C40-C41)

C40.91

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

Malignant neoplasm of unspecified bones and articular cartilage of right limb

Cancer of bone or cartilage in the right arm or leg when the exact location within that limb is not identified.

Buddy the Bee presenting code insight

Buddy Insight

Primary malignant neoplasm of unspecified bones and articular cartilage of the right limb.

CMS-HCC V28

HCC 21

RAF 0.671

CMS-HCC V24

HCC 10

RAF 0.675

ACA/HHS

HCC 10

Varies by metal level

ESRD/PACE

HCC 10

RAF 0.111

RXHCC

HCC 22

RAF 0.124

Code Book Path

Official
C40Malignant neoplasm of bone and articular cartilage of limbs
C40.9Malignant neoplasm of unspecified bones and articular cartilage of limb
C40.91Malignant neoplasm of unspecified bones and articular cartilage of right limb

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C40.91 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C40.91 in this effective period.

Related Child Codes

Official
C40.90Malignant neoplasm of unspecified bones and articular cartilage of unspecified limb
C40.92Malignant neoplasm of unspecified bones and articular cartilage of left limb

Includes

Official

ICD-10-CM does not list Includes notes for C40.91 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C40.91 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C40.91 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C40.91 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C40.91 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Right-side laterality documented
Provider query for specific bone location (short vs. long bones, specific bone name)
Histologic type from pathology
Primary vs. metastatic origin confirmed

MEAT Support

HCC Buddy guidance
Right-side laterality documented
Provider query for specific bone location (short vs. long bones, specific bone name)
Histologic type from pathology
Primary vs. metastatic origin confirmed

Audit Caution

HCC Buddy guidance
Using this code when imaging or operative reports specify the exact bone involved — always code to the highest specificity
Confusing right limb unspecified bone (C40.91) with unspecified right limb site with overlapping involvement (C40.81)
Not reviewing all available records for bone-specific information before settling on an unspecified code
Coding metastatic right limb bone lesions as primary malignancy

Common Mistakes

HCC Buddy guidance
C40.92 — Unspecified bones of LEFT limb; opposite laterality
C40.90 — Unspecified bones of UNSPECIFIED limb; less specific version
C40.01/C40.11/C40.21/C40.31 — Specific right-sided bone codes; use when exact bone type is known
C41.9 — Bone/cartilage unspecified; for non-limb locations or completely unspecified

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 C40.91 an HCC code?

Yes. C40.91 (Malignant neoplasm of unspecified bones and articular cartilage of right limb) maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24), with a community non-dual aged RAF of 0.671. It is billable for payment year 2026.

Coder answer: C40.91 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
C40.91
Description
Malignant neoplasm of unspecified bones and articular cartilage of right limb
HCC (V28)
HCC 21 — Lymphoma and Other Cancers
RAF
0.671
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers
0.671
V24HCC 10, Lymphoma and Other Cancers
0.675
ESRDHCC 10, Lymphoma and Other Cancers
0.111
RxHCCHCC 22, Cancer, Other Specified Sites
0.124

Each model's RAF is its CMS base weight for that model's standard population, so 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 segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work C40.91 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C40.91

For C40.91 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

  • 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

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C40.91 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C40.91 is the ICD-10-CM diagnosis code for malignant neoplasm of unspecified bones and articular cartilage of right limb. Cancer of bone or cartilage in the right arm or leg when the exact location within that limb is not identified. C40.91 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of bone and articular cartilage (c40-c41).

Under the CMS-HCC V28 risk adjustment model, C40.91 maps to Lymphoma and Other Cancers (HCC 21) with a community, non-dual, aged base RAF weight of 0.671. Under the older V24 model, C40.91 mapped to the same category but with a base RAF weight of 0.675, V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Confirm right limb is documented; this code is used when specific bone site is unspecified. Because C40.91 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for C40.91 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Confirm right limb is documented; this code is used when specific bone site is unspecified
  • •If more specific bone location is documented, use a more specific C40 code instead

Clinical Significance

Primary malignant neoplasm of unspecified bones and articular cartilage of the right limb. While laterality is specified as right, the exact bone location is not identified. This code is used when documentation confirms right-sided limb involvement but does not specify whether short bones, long bones, or overlapping sites are affected.

Documentation Requirements

  • ✓Right-side laterality documented
  • ✓Provider query for specific bone location (short vs. long bones, specific bone name)
  • ✓Histologic type from pathology
  • ✓Primary vs. metastatic origin confirmed
  • ✓Imaging findings that might clarify the bone site
  • ✓Treatment status and disease progression

Commonly Confused Codes

  • •C40.92: Unspecified bones of LEFT limb; opposite laterality
  • •C40.90: Unspecified bones of UNSPECIFIED limb; less specific version
  • •C40.01/C40.11/C40.21/C40.31: Specific right-sided bone codes; use when exact bone type is known
  • •C41.9: Bone/cartilage unspecified; for non-limb locations or completely unspecified

Child Codes

C40.90Malignant neoplasm of unspecified bones and articular cartilage of unspecified limb
HCC 21
C40.91Malignant neoplasm of unspecified bones and articular cartilage of right limb
HCC 21
C40.92Malignant neoplasm of unspecified bones and articular cartilage of left limb
HCC 21

Code Hierarchy

└C40Malignant neoplasm of bone and articular cartilage of limbs└C40.9Malignant neoplasm of unspecified bones and articular cartilage of limb└C40.91Malignant neoplasm of unspecified bones and articular cartilage of right limb
└C40.91Malignant neoplasm of unspecified bones and articular cartilage of right limb

Because C40.91 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

C40.91 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. Because C40.91 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

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