M31.8
BillableOther specified necrotizing vasculopathies
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M31.8 an HCC code?
Yes. M31.8 maps to Reactive and Specified Arthropathies under the CMS-HCC V28 risk adjustment model (and Vascular Disease under V24).
HCC Category Mapping
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 M31.8
For M31.8to 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 M31.8 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M31.8 is the ICD-10-CM diagnosis code for other specified necrotizing vasculopathies. Other types of blood vessel inflammation and damage that don't fit into more specific vasculitis categories. M31.8 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, M31.8 maps to Reactive and Specified Arthropathies (HCC 94) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, M31.8 maps to Vascular Disease (HCC 108) with a community, non-dual, aged base RAF weight of 0.297. 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 specific type of necrotizing vasculopathy is documented but doesn't fit other M31 codes. Because M31.8 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 M31.8 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 specific type of necrotizing vasculopathy is documented but doesn't fit other M31 codes
- •Include documentation of which blood vessels are affected and what organs are involved for complete coding
Clinical Significance
This diagnosis represents a serious systemic vasculitis that can affect multiple organ systems and requires ongoing monitoring and treatment. The condition significantly impacts patient morbidity and mortality risk, requiring specialized care coordination and frequent monitoring for complications.
Documentation Requirements
- ✓Documentation of necrotizing vasculopathy diagnosis by a rheumatologist or other specialist
- ✓Specific type of vasculopathy that doesn't fit other M31 categories
- ✓Laboratory evidence supporting vasculitis (elevated ESR, CRP, ANCA if applicable)
- ✓Imaging studies showing vascular involvement (angiography, CT, MRI)
- ✓Biopsy results confirming necrotizing inflammation when available
- ✓Documentation of affected organ systems or vessels
- ✓Current treatment regimen and response to therapy
- ✓Any complications or sequelae from the vasculopathy
Commonly Confused Codes
- •M31.9 — Use when the type of necrotizing vasculopathy is unspecified rather than a specified other type
- •M31.0-M31.7 — Use specific codes when the vasculopathy fits defined categories like polyarteritis nodosa or Wegener's
- •I77.6 — Use for arteritis when there's no evidence of necrotizing vasculopathy
- •M35.2 — Use for Behçet's disease rather than other specified necrotizing vasculopathies