C84.03 ICD-10-CM Code: Mycosis fungoides, intra-abdominal lymph nodes
C84.03 maps to CMS-HCC V28 20. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools
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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lymphoid, hematopoietic and related tissue (C81-C96)
C84.03
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMycosis fungoides, intra-abdominal lymph nodes
Mycosis fungoides is a type of blood cancer that starts in skin T-cells and has spread to the lymph nodes inside the abdomen. This is an advanced stage of the disease where cancer cells are found in the abdominal lymph node region.
Buddy Insight
Mycosis fungoides with intra-abdominal lymph node involvement indicates significant disease progression with visceral lymph node spread.
CMS-HCC V28
MappedHCC 20
Coefficient HCC 20: 1.136 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 010
Code-level coefficient reference
ESRD/PACE
MappedHCC 10
Code-level coefficient reference
RXHCC
MappedHCC 19
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for C84.03. Check the code and parent instructions in the Code Book.
Excludes 2
Official- Kaposi's sarcoma of lymph nodes (C46.3)Inherited from C81-C96
- secondary and unspecified neoplasm of lymph nodes (C77.-)Inherited from C81-C96
- secondary neoplasm of bone marrow (C79.52)Inherited from C81-C96
- secondary neoplasm of spleen (C78.89)Inherited from C81-C96
Related Codes
Includes
OfficialNo Includes notes are included in this display for C84.03. Check the code and parent instructions in the Code Book.
Excludes 1
Official- personal history of non-Hodgkin lymphoma (Z85.72)Inherited from C84, C84.0
- peripheral T-cell lymphoma, not elsewhere classified (C84.4-)Inherited from C84, C84.0
Code First
OfficialNo Code First sequencing instructions are included in this display for C84.03. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for C84.03. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for C84.03. Check the code and parent instructions in the Code Book.
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 C84.03 an HCC code?
Yes. C84.03 (Mycosis fungoides, intra-abdominal lymph nodes) maps to HCC 20, Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 1.136. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: C84.03 is billable and maps to V28 HCC 20, Lung and Other Severe Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- C84.03
- Description
- Mycosis fungoides, intra-abdominal lymph nodes
- HCC (V28)
- HCC 20 — Lung and Other Severe Cancers
- RAF reference coefficient
- 1.136
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work C84.03 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C84.03
For C84.03, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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What This Code Means
C84.03 is the ICD-10-CM diagnosis code for mycosis fungoides, intra-abdominal lymph nodes. Mycosis fungoides is a type of blood cancer that starts in skin T-cells and has spread to the lymph nodes inside the abdomen. This is an advanced stage of the disease where cancer cells are found in the abdominal lymph node region. C84.03 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, C84.03 maps to Lung and Other Severe Cancers (HCC 20) with a source-labeled community, non-dual, aged reference coefficient of 1.136. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Verify documentation specifies the lymph node location as intra-abdominal; if lymph nodes are in other locations (peripheral, mediastinal, etc.), use different C84.0x subcodes. For C84.03, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, and MEAT documentation criteria for C84.03 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify documentation specifies the lymph node location as intra-abdominal; if lymph nodes are in other locations (peripheral, mediastinal, etc.), use different C84.0x subcodes
- •Mycosis fungoides requires staging information; ensure the stage is documented and coded separately if applicable, as this code alone does not capture disease stage
Clinical Significance
Mycosis fungoides with intra-abdominal lymph node involvement indicates significant disease progression with visceral lymph node spread. Abdominal lymph node involvement in mycosis fungoides is associated with advanced staging and poor prognosis, requiring aggressive systemic therapy. This presentation is uncommon and represents transformation from early-stage cutaneous disease.
Documentation Requirements
- ✓Skin biopsy confirming mycosis fungoides
- ✓Abdominal imaging (CT or PET/CT) documenting intra-abdominal lymphadenopathy
- ✓Pathologic confirmation of nodal involvement if biopsy obtained
- ✓TNMB staging reflecting visceral lymph node disease
- ✓Treatment plan addressing advanced-stage disease
Commonly Confused Codes
- •C84.09: Mycosis fungoides, extranodal: Use when abdominal organs (not lymph nodes) are involved
- •C84.00: Mycosis fungoides, unspecified site: Use C84.03 when intra-abdominal nodal disease is confirmed
- •C83.93: Non-follicular lymphoma, unspecified, intra-abdominal: For non-follicular lymphoma, not mycosis fungoides