C96.5 ICD-10-CM Code: Multifocal and unisystemic Langerhans-cell histiocytosis
C96.5 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 lymphoid, hematopoietic and related tissue (C81-C96)
C96.5
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMultifocal 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.
Buddy Insight
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.
CMS-HCC V28
MappedHCC 21
RAF 0.671
CMS-HCC V24
MappedHCC 10
RAF 0.675
ACA/HHS
MappedHCC 10
Varies by metal level
ESRD/PACE
MappedHCC 10
RAF 0.111
RXHCC
MappedHCC 21
RAF 0.410
Code Book Path
Inclusion Terms
Official- Hand-Schüller-Christian disease
- Histiocytosis X, multifocal
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for C96.5 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for C96.5 in this effective period.
Excludes 1
Official- multifocal and multisystemic (disseminated) Langerhans-cell histiocytosis (C96.0)
- unifocal Langerhans-cell histiocytosis (C96.6)
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for C96.5 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for C96.5 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for C96.5 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 C96.5 an HCC code?
Yes. C96.5 (Multifocal and unisystemic Langerhans-cell histiocytosis) 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: C96.5 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
- C96.5
- Description
- Multifocal and unisystemic Langerhans-cell histiocytosis
- HCC (V28)
- HCC 21 — Lymphoma and Other Cancers
- RAF
- 0.671
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 C96.5 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
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.
Coder workflow notes
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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 Lymphoma and Other Cancers (HCC 21) with a community, non-dual, aged base RAF weight of 0.671. Under the older V24 model, C96.5 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.
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.
Excludes 1, Do NOT code together
Commonly Confused Codes
- •C96.0 (multifocal and multisystemic Langerhans-cell histiocytosis) involves multiple organ systems rather than just one
- •C96.6 (unifocal Langerhans-cell histiocytosis) is limited to a single site
- •D76.3 (other histiocytosis syndromes) covers non-malignant histiocytic disorders that do not fit Langerhans-cell criteria.