What is ICD-10 code C84.10?

C84.10 is the ICD-10-CM diagnosis code for Sezary 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. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C84.10 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C84.10 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C84.10 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C84.10 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for C84.10?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C84.10, V28 maps to Metastatic Cancer and Acute Leukemia at RAF 0.368 while V24 mapped to Lymphoma and Other Cancers at RAF 0.675. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C84.10?

Use this code only when the site of lymph node involvement cannot be determined from documentation If site is documented, use a more specific code (C84.11-C84.16) instead Because C84.10 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.

C84.10 ICD-10 Code: Sezary disease, unspecified

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC84.10Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lymphoid, hematopoietic and related tissue (C81-C96)

C84.10

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

Sezary 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.

Buddy Insight

CMS-HCC V28

Mapped

HCC 17

Metastatic Cancer and Acute L...

RAF 0.368

CMS-HCC V24

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.675

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.0

RXHCC

Mapped

HCC 19

Lymphoma and Other Cancers

RAF 0.0

Code Trumping

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Compare selected patient codes to show trumped or trumps impact.

Code Book Path

Official

C84Mature T/NK-cell lymphomas

C84.1Sezary disease

C84.10Sezary disease, unspecified site

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C84.10 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C84.10 in this effective period.

Related Child Codes

Official

C84.11Sezary disease, lymph nodes of head, face, and neck

C84.12Sezary disease, intrathoracic lymph nodes

C84.13Sezary disease, intra-abdominal lymph nodes

C84.14Sezary disease, lymph nodes of axilla and upper limb

C84.15Sezary disease, lymph nodes of inguinal region and lower limb

Includes

Official

ICD-10-CM does not list Includes notes for C84.10 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C84.10 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C84.10 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C84.10 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C84.10 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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

MEAT Support

HCC Buddy guidance

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

Audit Caution

HCC Buddy guidance

Coding Sezary disease as mycosis fungoides — they are clinically and prognostically distinct entities despite both being cutaneous T-cell lymphomas

Using dermatitis codes for the skin manifestations of Sezary disease instead of the lymphoma code

Not verifying the presence of circulating Sezary cells in blood work, which is required to distinguish Sezary from erythrodermic mycosis fungoides

Confusing reactive erythroderma with Sezary disease — blood work is essential for diagnosis

Common Mistakes

HCC Buddy guidance

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

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

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

V28HCC 17, Metastatic Cancer and Acute Leukemia

0.368

V24HCC 10, Lymphoma and Other Cancers

0.675

ESRDHCC 10, Lymphoma and Other Cancers

0.000

RxHCCHCC 19, Lymphoma and Other Cancers

0.000

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 C84.10to 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 sezary 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

•Use this code only when the site of lymph node involvement cannot be determined from documentation
•If site is documented, use a more specific code (C84.11-C84.16) instead

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