D89.84 ICD-10-CM Code: IgG4-related disease
HCC Buddy Code Card
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FY 2026 Apr update / Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (D50-D89) / Certain disorders involving the immune mechanism (D80-D89)
D89.84
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceIgG4-related disease
A chronic inflammatory condition where IgG4 antibodies accumulate in various organs, causing inflammation, fibrosis, and organ dysfunction.
Buddy Insight
IgG4-related disease is a chronic fibro-inflammatory condition characterized by tumefactive lesions with dense lymphoplasmacytic infiltration rich in IgG4-positive plasma cells, storiform fibrosis, and often elevated serum IgG4 levels.
CMS-HCC V28
MappedHCC 115
RAF 0.565
CMS-HCC V24
MappedHCC 47
RAF 0.665
ACA/HHS
MappedHCC 74
Varies by metal level
ESRD/PACE
MappedHCC 47
RAF 0.078
RXHCC
MappedHCC 99
RAF 0.943
Code Book Path
Inclusion Terms
Official- Immunoglobulin G4-related disease
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for D89.84 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for D89.84 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for D89.84 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for D89.84 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for D89.84 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for D89.84 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 D89.84 an HCC code?
Yes. D89.84 (IgG4-related disease) maps to Specified Immunodeficiencies and White Blood Cell Disorders under the CMS-HCC V28 risk adjustment model (and Disorders of Immunity under V24), with a community non-dual aged RAF of 0.565. It is billable for payment year 2026.
Coder answer: D89.84 is billable and maps to V28 HCC 115, Specified Immunodeficiencies and White Blood Cell Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- D89.84
- Description
- IgG4-related disease
- HCC (V28)
- HCC 115 — Specified Immunodeficiencies and White Blood Cell Disorders
- RAF
- 0.565
- 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 D89.84 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for D89.84
For D89.84 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 D89.84 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
D89.84 is the ICD-10-CM diagnosis code for igg4-related disease. A chronic inflammatory condition where IgG4 antibodies accumulate in various organs, causing inflammation, fibrosis, and organ dysfunction. D89.84 sits in the ICD-10-CM chapter for diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (d50-d89), within the section covering certain disorders involving the immune mechanism (d80-d89).
Under the CMS-HCC V28 risk adjustment model, D89.84 maps to Specified Immunodeficiencies and White Blood Cell Disorders (HCC 115) with a community, non-dual, aged base RAF weight of 0.565. Under the older CMS-HCC V24 model, D89.84 maps to Disorders of Immunity (HCC 47) with a community, non-dual, aged base RAF weight of 0.665. 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.
Document which organ systems are involved (pancreas, salivary glands, lungs, etc.) as this affects clinical management. Because D89.84 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 D89.84 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Document which organ systems are involved (pancreas, salivary glands, lungs, etc.) as this affects clinical management
- •Ensure elevated serum IgG4 levels and tissue biopsy findings are documented to support the diagnosis
Clinical Significance
IgG4-related disease is a chronic fibro-inflammatory condition characterized by tumefactive lesions with dense lymphoplasmacytic infiltration rich in IgG4-positive plasma cells, storiform fibrosis, and often elevated serum IgG4 levels. It can affect virtually any organ, most commonly the pancreas (autoimmune pancreatitis), salivary glands, lacrimal glands, retroperitoneum, and kidneys. Despite its often indolent course, untreated disease leads to progressive organ damage and fibrosis.
Documentation Requirements
- ✓Documentation must confirm IgG4-related disease with supporting evidence including elevated serum IgG4 levels, characteristic histopathologic features on biopsy (dense IgG4-positive plasma cell infiltrate, storiform fibrosis, obliterative phlebitis), and affected organ systems.
- ✓The American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria should be referenced.
- ✓Treatment with corticosteroids or rituximab and response should be documented.
Commonly Confused Codes
- •K86.1 (Other chronic pancreatitis) may be assigned for autoimmune pancreatitis without recognizing IgG4-related disease as the underlying cause. C85.9
- •(Non-Hodgkin lymphoma) can mimic IgG4-related disease with lymphoid infiltrates. D89.89 (Other specified disorders involving the immune mechanism) is less specific. E06.5 (Other chronic thyroiditis) may be used for Riedel thyroiditis, which is now considered part of the IgG4-related disease spectrum.