M31.9 ICD-10-CM Code: Necrotizing vasculopathy, unspecified
M31.9 maps to CMS-HCC V28 94 (RAF 0.268). 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)
M31.9
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceNecrotizing vasculopathy, unspecified
Blood vessel inflammation and damage of an unspecified type affecting various parts of the body.
Buddy Insight
This unspecified necrotizing vasculopathy diagnosis indicates serious systemic vascular inflammation that requires intensive monitoring and treatment.
CMS-HCC V28
MappedHCC 94
RAF 0.268
CMS-HCC V24
MappedHCC 108
RAF 0.288
ACA/HHS
N/A—
Not mapped
ESRD/PACE
MappedHCC 108
RAF 0.073
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M31.9 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M31.9 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M31.9 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M31.9 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M31.9 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M31.9 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M31.9 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 M31.9 an HCC code?
Yes. M31.9 (Necrotizing vasculopathy, unspecified) maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders under the CMS-HCC V28 risk adjustment model (and Vascular Disease under V24), with a community non-dual aged RAF of 0.268. It is billable for payment year 2026.
Coder answer: M31.9 is billable and maps to V28 HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- M31.9
- Description
- Necrotizing vasculopathy, unspecified
- HCC (V28)
- HCC 94 — Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders
- RAF
- 0.268
- 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 M31.9 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for M31.9
For M31.9 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 M31.9 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
M31.9 is the ICD-10-CM diagnosis code for necrotizing vasculopathy, unspecified. Blood vessel inflammation and damage of an unspecified type affecting various parts of the body. M31.9 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, M31.9 maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders (HCC 94) with a community, non-dual, aged base RAF weight of 0.268. Under the older CMS-HCC V24 model, M31.9 maps to Vascular Disease (HCC 108) with a community, non-dual, aged base RAF weight of 0.288. 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.
This is a catch-all code; attempt to obtain more specific diagnosis information from the provider before coding. Because M31.9 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 M31.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a catch-all code; attempt to obtain more specific diagnosis information from the provider before coding
- •If vasculitis type can be determined through clinical findings or testing, use a more specific M31 code instead
Clinical Significance
This unspecified necrotizing vasculopathy diagnosis indicates serious systemic vascular inflammation that requires intensive monitoring and treatment. The unspecified nature suggests either incomplete workup or atypical presentation that doesn't fit standard vasculitis categories.
Documentation Requirements
- ✓Clear documentation of necrotizing vasculopathy diagnosis
- ✓Evidence that the specific type cannot be determined or is atypical
- ✓Laboratory findings consistent with systemic vasculitis
- ✓Imaging or biopsy evidence of necrotizing vascular inflammation
- ✓Documentation of affected vessels or organ systems
- ✓Treatment plan and patient response to therapy
- ✓Any complications from the vasculopathy
- ✓Reason why a more specific code cannot be assigned