ICD-10 Code M31.0: Hypersensitivity angiitis diagnosis and billing

Key takeaways

ICD-10 Code M31.0 is a billable ICD-10-CM diagnosis code for hypersensitivity angiitis, valid for encounters from October 1, 2025 (FY2026).

M31.0 classifies under category M31 (Other necrotizing vasculopathies) within block M30-M36 (Systemic connective tissue disorders).

Goodpasture’s syndrome is the only inclusion term the FY2026 tabular list carries under M31.0.

Leukocytoclastic vasculitis and allergic vasculitis reach M31.0 through the Alphabetic Index, and M31.0 carries no excludes notes.

Practice management software like Pabau keeps the vessel size, biopsy findings, and ANCA status in the note behind M31.0.

ICD-10 Code M31.0 is a billable ICD-10-CM diagnosis code for hypersensitivity angiitis, an immune-mediated inflammation of small blood vessels. In fact, the FY2026 tabular list carries exactly one inclusion term under it: Goodpasture’s syndrome. In addition, it carries no Excludes1 or Excludes2 note at all.

The terms clinicians actually write are a different matter. Leukocytoclastic vasculitis and allergic vasculitis both reach M31.0, but through the Alphabetic Index rather than a tabular inclusion note. That distinction decides how much documentation a coder needs before selecting the code.

In short, this reference covers billable status, code hierarchy, synonyms, excludes notes, related M31 codes, and FY2026 documentation requirements.

ICD-10 Code M31.0: billable status and effective date

ICD-10 Code M31.0 is a billable, specific ICD-10-CM diagnosis code. Specifically, it became effective on October 1, 2025 under the FY2026 edition of the CDC/NCHS ICD-10-CM code set. In other words, billable means the code goes on a claim as it stands, with no further subdivision required.

Coders can pull M31.0 straight from the encounter record when they document hypersensitivity angiitis. In practice, a medical records system that holds the code list next to the note removes the separate lookup step.

Clinical description: hypersensitivity angiitis

Hypersensitivity angiitis is an immune-mediated inflammation of small blood vessels, triggered by an antigen-antibody reaction. Specifically, it sits within the necrotizing vasculopathies and mainly affects postcapillary venules in the skin. In more severe cases, systemic presentations also reach the kidneys, lungs, and peripheral nerves.

Goodpasture’s syndrome sits under M31.0 as the tabular’s inclusion term, and it presents very differently. Specifically, it is an anti-glomerular basement membrane disease with pulmonary hemorrhage and rapidly progressive kidney failure. As a result, a coder who only expects skin findings under M31.0 will query a pulmonary-renal case unnecessarily.

In dermatology, the diagnosis usually arrives as palpable purpura: non-blanching, raised lesions on the lower extremities. Specifically, a skin biopsy showing leukocytoclasia (nuclear dust from fragmented neutrophils) and fibrinoid necrosis in the vessel walls gives the histological confirmation. Accordingly, practices running dermatology EMR software can file that biopsy report against the same encounter as the code.

• Primary presentation: Palpable purpura, urticaria, or vesiculobullous lesions on dependent areas
• Systemic involvement: Renal, pulmonary, and joint involvement in more severe cases
• Common triggers: Drug hypersensitivity, infections, and connective tissue diseases
• Histology: Leukocytoclasia, fibrinoid necrosis, and perivascular neutrophilic infiltrate on skin biopsy

Synonyms and aliases for hypersensitivity angiitis

The FY2026 tabular list carries one inclusion term under M31.0: Goodpasture’s syndrome. Everything else coders see in records reaches the code through the Alphabetic Index instead. As a result, knowing which route a term takes is what stops a miscoded encounter.

Not every leukocytoclastic vasculitis case ends at M31.0. For example, drug-induced LCV usually needs an additional adverse-effect code for the causative agent. Microscopic polyangiitis has its own code, so a record naming MPA belongs on M31.7. In short, code what the provider named, not the pattern the biopsy showed.

Where M31.0 sits in the ICD-10-CM hierarchy

M31.0 is a fourth-character code, the most specific level in this branch of ICD-10-CM. The hierarchy is worth knowing when documentation is ambiguous and you need the right parent or sibling to query against.

Category M31 has no non-billable parent that would demand more specificity from M31.0. When a provider documents “other necrotizing vasculopathy” without naming a subtype, query rather than default to M31.0. In practice, the CMS ICD-10 codes page hosts the official FY2026 tabular list.

Includes and excludes notes for M31.0

M31.0 carries one Includes note and no excludes notes at all. In fact, that is worth stating plainly. However, several coding resources publish excludes notes for M31.0 that the tabular list does not contain.

Includes notes

The FY2026 tabular list carries a single inclusion term under M31.0: Goodpasture’s syndrome. In other words, an inclusion term is not a separate code. A record documenting Goodpasture’s syndrome is coded M31.0, and the renal and pulmonary manifestations are coded separately where the provider documents them.

Excludes1 notes

M31.0 has no Excludes1 note in the FY2026 tabular list. Specifically, the only Excludes1 in category M31 sits under M31.7, which excludes polyarteritis nodosa (M30.0). Excludes1 is a strict never-code-together rule, so it never blocks an M31.0 line on its own. Accordingly, confirm this against the CDC/NCHS ICD-10-CM tool at the start of each fiscal year.

Excludes2 notes

M31.0 has no Excludes2 note either. Excludes2 tells you an excluded condition is not part of the code but may coexist and be reported separately. Still, its absence here is not permission to report a second vasculitis code.

When a patient has hypersensitivity angiitis and a separately documented ANCA-associated condition, both codes can go on the claim. In that case, each diagnosis needs its own documented support in the record. Teams working through medical office compliance checks should confirm both entries before dual-coding.

Related ICD-10 codes in the M31 vasculitis family

Several siblings and near neighbors sit around M31.0 in rheumatology and dermatology records. Specifically, the table below separates the ones coders confuse most often. Systemic vasculitis outside category M31, such as M35.2, is coded from its own category.

The AAPC code lookup is a quick way to confirm a sibling’s full descriptor. Check it before you settle for a less specific alternative.

Documentation requirements for accurate M31.0 coding

Most M31.0 denials come back to a record that names “vasculitis” and stops there. Instead, payers reviewing the diagnosis expect the clinical evidence behind the code. For that reason, practices using digital intake forms can build note templates that prompt for every field below.

• Vasculitis type named: The provider documents “hypersensitivity angiitis,” “leukocytoclastic vasculitis,” “allergic vasculitis,” or “Goodpasture’s syndrome” rather than a generic “vasculitis”
• Vessel size and site: Small vessel involvement, plus the organ or tissue affected (skin, kidney, lung)
• Biopsy findings: Leukocytoclasia, fibrinoid necrosis, and perivascular neutrophilic infiltrate support the specificity of the code
• Trigger or etiology: Whether a drug, infection, or autoimmune condition caused it, since that decides whether an additional etiology code applies
• Differential considered: Note where granulomatosis with polyangiitis or polyarteritis nodosa was ruled out, which supports the M31.0 selection
• ANCA status: Record the result where tested, because a positive ANCA may point to M31.7 or the M31.3x series instead

The trigger is often documented before the vasculitis is. For example, primary care records the drug started three weeks ago, or the streptococcal throat infection that preceded the rash. Accordingly, practices on GP clinic software should make sure the referral letter carries that detail.

Capturing all of this at the point of care beats a retrospective query every time. In turn, building the prompts into the note template keeps records audit-ready, which is the wider point of HIPAA compliance software.

Code history and annual updates

M31.0 has been stable across recent fiscal years. In fact, FY2026 brought no revision to the description, the inclusion term, or the hierarchy. Specifically, the table below summarizes the code history from published CMS update documentation.

Confirm the current edition each October against the official CMS listing. In turn, any change to the M31.0 description or hierarchy is published there. Run the same check over your other high-volume rheumatology codes, such as M17.5 and M18.4.

How Pabau supports vasculitis coding and documentation

Vasculitis coding is unforgiving of a vague note. For example, a rheumatology practice seeing 15 to 20 vasculitis patients a week builds a query backlog fast. That happens whenever the note template never asks for vessel size or ANCA status.

Practice management software like Pabau lets clinicians search a diagnosis code from inside the encounter record. As a result, M31.0 no longer needs a separate lookup tool open alongside the note. In addition, templated SOAP notes, short for subjective, objective, assessment and plan, can prompt for vessel size, biopsy result, trigger, and ANCA status.

Pabau Scribe, our AI scribe, drafts the note from the consultation itself. Spoken detail about the biopsy or the drug history lands in the record rather than in someone’s memory. The result is a documented encounter that stands up when a payer asks what supports M31.0.

Complete documentation before the encounter closes

Pabau brings diagnosis code search, templated notes, and patient records into one system. Every field a vasculitis diagnosis needs is prompted at the visit, not chased later.

Book a demo

Conclusion

M31.0 comes with a short rule set. It carries one inclusion term and no excludes notes, and the M31 category offers a more accurate sibling whenever ANCA is positive.

The harder part is the note behind the code. Specifically, a record naming the subtype, the vessel size, and the trigger survives review. By contrast, a record that says “vasculitis” and stops there will not.

Build those prompts into the template once and the coding takes care of itself for every vasculitis encounter after that. Book a demo to see how Pabau captures the documentation an M31.0 encounter needs.

Continue your research

Coding another high-volume musculoskeletal diagnosis? M54.2 walks through the documentation a cervicalgia claim needs.

Working with an unspecified diagnosis code? M27.9 shows how much detail an unspecified code still expects in the record.

Billing a skin lesion procedure alongside the diagnosis? 11312 covers lesion size, site, and the documentation that supports it.

Documenting the biopsy that confirms the diagnosis? 20251 covers the operative detail an open biopsy claim needs.

Frequently asked questions