C84.10
BillableSézary disease, unspecified site
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C84.10 an HCC code?
Yes. C84.10 maps to Metastatic Cancer and Acute Leukemia 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 C84.10
For C84.10 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 C84.10 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C84.10 is the ICD-10-CM diagnosis code for sézary disease, unspecified site. Sézary disease, an aggressive form of skin cancer involving abnormal white blood cells, when the specific location of lymph node involvement is not specified. C84.10 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, C84.10 maps to Metastatic Cancer and Acute Leukemia (HCC 17) with a community, non-dual, aged base RAF weight of 0.368. Under the older CMS-HCC V24 model, C84.10 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.
Use this code only when the site of lymph node involvement cannot be determined from documentation. Because C84.10 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 C84.10 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
Sezary disease at an unspecified site is an aggressive leukemic variant of cutaneous T-cell lymphoma characterized by erythroderma (generalized skin redness affecting most of the body surface), lymphadenopathy, and circulating malignant T-cells (Sezary cells) in the peripheral blood. It is classified as Stage IVA or higher and carries a significantly worse prognosis than mycosis fungoides, with median survival of 2-4 years.
Documentation Requirements
- ✓Skin biopsy confirming cutaneous T-cell lymphoma
- ✓Peripheral blood flow cytometry or morphology demonstrating circulating Sezary cells (atypical T-cells with cerebriform nuclei)
- ✓Documentation of erythroderma with body surface area involvement
- ✓Lymph node assessment and staging documentation
- ✓Treatment plan — typically systemic therapy required
Commonly Confused Codes
- •C84.00 — Mycosis fungoides, unspecified site: Mycosis fungoides is primarily cutaneous without significant blood involvement; Sezary disease requires circulating malignant T-cells
- •C84.40 — Peripheral T-cell lymphoma, unspecified: Sezary disease is a specific form of T-cell lymphoma with defined diagnostic criteria
- •L53.9 — Erythematous condition, unspecified: Erythroderma from Sezary disease should be coded with the lymphoma code, not a dermatologic code