C40.91
BillableMalignant neoplasm of unspecified bones and articular cartilage of right limb
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C40.91 an HCC code?
Yes. C40.91 maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for C40.91
For C40.91to 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.
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