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M31.0 ICD-10-CM Code: Hypersensitivity angiitis

M31.0 maps to CMS-HCC V28 93. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Systemic connective tissue disorders (M30-M36)

M31.0

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

Hypersensitivity angiitis

An allergic reaction affecting blood vessels that causes inflammation and tissue damage, typically triggered by medications or infections.

Buddy the Bee presenting code insight

Buddy Insight

Hypersensitivity angiitis represents a drug-induced or infection-triggered small vessel vasculitis that typically affects skin and may involve other organs.

CMS-HCC V28

HCC 93

Code-level coefficient reference

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 056

Code-level coefficient reference

ESRD/PACE

HCC 40

Code-level coefficient reference

RXHCC

HCC 84

Code-level coefficient reference

Code Book Path

Official
M31Other necrotizing vasculopathies
M31.0Hypersensitivity angiitis

Inclusion Terms

Official
  • Goodpasture's syndrome

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M31.0 in this effective period.

Related Child Codes

Official
M31.1Thrombotic microangiopathy
M31.2Lethal midline granuloma
M31.3Wegener's granulomatosis
M31.4Aortic arch syndrome [Takayasu]
M31.5Giant cell arteritis with polymyalgia rheumatica

Includes

Official

ICD-10-CM does not list Includes notes for M31.0 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M31.0 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M31.0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M31.0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M31.0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Clinical evidence of small vessel vasculitis
Documentation of suspected triggering agent (drug, infection)
Skin biopsy showing leukocytoclastic vasculitis
Timeline relating exposure to symptom onset

MEAT Support

HCC Buddy guidance
Clinical evidence of small vessel vasculitis
Documentation of suspected triggering agent (drug, infection)
Skin biopsy showing leukocytoclastic vasculitis
Timeline relating exposure to symptom onset

Audit Caution

HCC Buddy guidance
Using when systemic vasculitis is present
Confusing with cutaneous-only vasculitis
Missing the hypersensitivity/allergic component
Using anaphylaxis codes for vasculitic reactions

Common Mistakes

HCC Buddy guidance
L95.9 — Vasculitis limited to skin, unspecified (when only skin involvement)
M30.0 — Polyarteritis nodosa (medium vessel involvement)
M31.7 — Microscopic polyangiitis (systemic small vessel vasculitis)
T88.6 — Anaphylactic reaction due to adverse effect of correct drug (acute allergic reaction)

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 M31.0 an HCC code?

Yes. M31.0 (Hypersensitivity angiitis) maps to HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.617. 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: M31.0 is billable and maps to V28 HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
M31.0
Description
Hypersensitivity angiitis
HCC (V28)
HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
RAF reference coefficient
0.617
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
0.617
ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
Not separately weighted
RxHCCHCC 84, Systemic Lupus Erythematosus and Other Systemic Connective Tissue Disorders
Not separately weighted

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 M31.0 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for M31.0

For M31.0 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 M31.0 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M31.0 is the ICD-10-CM diagnosis code for hypersensitivity angiitis. An allergic reaction affecting blood vessels that causes inflammation and tissue damage, typically triggered by medications or infections. M31.0 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering systemic connective tissue disorders (m30-m36).

Under the CMS-HCC V28 risk adjustment model, M31.0 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a source-labeled community, non-dual, aged reference coefficient of 0.617. No V24 mapping is shown for M31.0; use the applicable model and payment year when reviewing the V28 mapping. 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. 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.

Document the triggering agent (drug, infection, or other cause) when possible. Because M31.0 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 M31.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Document the triggering agent (drug, infection, or other cause) when possible
  • •Distinguish from other vasculitides by the hypersensitivity mechanism

Clinical Significance

Hypersensitivity angiitis represents a drug-induced or infection-triggered small vessel vasculitis that typically affects skin and may involve other organs. While often less severe than systemic vasculitis, it requires identification and removal of triggering agents and monitoring for systemic involvement.

Documentation Requirements

  • ✓Clinical evidence of small vessel vasculitis
  • ✓Documentation of suspected triggering agent (drug, infection)
  • ✓Skin biopsy showing leukocytoclastic vasculitis
  • ✓Timeline relating exposure to symptom onset
  • ✓Assessment of organ involvement beyond skin
  • ✓Response to trigger removal or treatment
  • ✓Monitoring for recurrence
  • ✓Exclusion of systemic vasculitis syndromes

Commonly Confused Codes

  • •L95.9: Vasculitis limited to skin, unspecified (when only skin involvement)
  • •M30.0: Polyarteritis nodosa (medium vessel involvement)
  • •M31.7: Microscopic polyangiitis (systemic small vessel vasculitis)
  • •T88.6: Anaphylactic reaction due to adverse effect of correct drug (acute allergic reaction)
  • •L27.0: Generalized skin eruption due to drugs and medicaments

Child Codes

M31.0Hypersensitivity angiitis
HCC 93
M31.1Thrombotic microangiopathy
M31.2Lethal midline granuloma
HCC 93
M31.3Wegener's granulomatosis
M31.4Aortic arch syndrome [Takayasu]
HCC 93
M31.5Giant cell arteritis with polymyalgia rheumatica
HCC 94
M31.6Other giant cell arteritis
HCC 94
M31.7Microscopic polyangiitis
HCC 94
M31.8Other specified necrotizing vasculopathies
HCC 94
M31.9Necrotizing vasculopathy, unspecified
HCC 94

Code Hierarchy

└M31Other necrotizing vasculopathies└M31.0Hypersensitivity angiitis
└M31.0Hypersensitivity angiitis

Because M31.0 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment.

M31.0 maps to CMS-HCC V28 category 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for M31.0. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

Work M31.0 in HCC Buddy

Open M31.0 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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