M31.9
BillableNecrotizing vasculopathy, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M31.9 an HCC code?
Yes. M31.9 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).
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 M31.9
For M31.9to 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.
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