C96.5
BillableMultifocal and unisystemic Langerhans-cell histiocytosis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C96.5 an HCC code?
Yes. C96.5 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors 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 C96.5
For C96.5 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 C96.5 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C96.5 is the ICD-10-CM diagnosis code for multifocal and unisystemic langerhans-cell histiocytosis. This is a rare blood disorder where abnormal immune cells called Langerhans cells multiply in multiple locations throughout the body but are limited to one organ system. It's a type of cancer-like condition that affects how the body's immune system functions. C96.5 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lymphoid, hematopoietic and related tissue (c81-c96).
Under the CMS-HCC V28 risk adjustment model, C96.5 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors (HCC 21) with a community, non-dual, aged base RAF weight of 0.545. Under the older CMS-HCC V24 model, C96.5 maps to Lymphoma and Other Cancers (HCC 10) with a community, non-dual, aged base RAF weight of 0.675. 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.
Verify whether the histiocytosis is truly multifocal (multiple sites) and unisystemic (single organ system) before assigning this code, as this distinction affects treatment planning and prognosis. Because C96.5 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 C96.5 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify whether the histiocytosis is truly multifocal (multiple sites) and unisystemic (single organ system) before assigning this code, as this distinction affects treatment planning and prognosis
- •Document the specific organ system involved (skin, bone, lungs, etc.) in the medical record, as this information may be needed for complete clinical documentation even though it's not required in the ICD-10 code itself
Clinical Significance
Multifocal and unisystemic Langerhans-cell histiocytosis is a rare proliferative disorder of dendritic cells that presents with lesions at multiple sites within a single organ system, most commonly bone or skin. Despite its benign-sounding classification, it carries significant morbidity due to tissue destruction and organ dysfunction, particularly in pediatric patients. This condition requires ongoing monitoring as it can progress to multisystem disease.
Documentation Requirements
- ✓Documentation must clearly specify that the disease is multifocal (affecting multiple sites) and unisystemic (confined to one organ system), with identification of the involved organ system.
- ✓Pathology confirmation with CD1a or CD207 (langerin) immunostaining is essential.
- ✓The provider should document the extent of involvement, treatment response, and any functional impairment.