Granulomatosis with polyangiitis (GPA/Wegener's) with confirmed renal involvement, such as glomerulonephritis — the more severe phenotype within the M31.3 subcategory.
Verified May 8, 2026 · 4 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 5
- Region
- General
Documentation tips
What should appear in the chart to support M31.31.
Source · Editorial brief grounded in 4 cited references ↓
- Explicitly state 'with renal involvement' or 'with glomerulonephritis' in the assessment — 'Wegener's granulomatosis NOS' maps to M31.30 by default.
- Record renal function lab values (creatinine, BUN, GFR) and urinalysis findings (hematuria, proteinuria, red cell casts) that support renal involvement.
- Document ANCA panel results — specifically PR3-ANCA (c-ANCA) positivity — as part of the diagnostic basis for GPA.
- If a renal biopsy was performed, document pathology results including presence of pauci-immune necrotizing glomerulonephritis.
- Note the current disease activity status (active vs. remission) and any current immunosuppressive therapy, which supports medical necessity for ongoing management visits.
Related CPT procedures
Procedure codes commonly billed with M31.31. Linking the right diagnosis to the right procedure is what establishes medical necessity.
Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis
Common coding pitfalls
The recurring mistakes coders make with M31.31 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Assigning M31.31 when the physician documents only 'Wegener's granulomatosis' or 'GPA NOS' without explicit renal involvement — index entries default those terms to M31.30.
- Confusing M31.31 with codes for primary glomerulonephritis (N00–N08) — if GPA with renal involvement is the confirmed diagnosis, M31.31 is correct and a separate glomerulonephritis code is not required.
- Using an outdated query term: 'Wegener's syndrome' indexes to M31.30 without renal qualifier — verify the note documents kidney involvement before stepping up to M31.31.
- Failing to capture M31.31 as a comorbidity on claims for nephrology or dialysis encounters when GPA is the underlying cause of renal disease.
Clinical context
Source · Editorial summary grounded in 4 cited references ↓
M31.31 is the billable code for Wegener's granulomatosis (now formally termed granulomatosis with polyangiitis, or GPA) when renal involvement is documented. Renal involvement typically means glomerulonephritis — confirmed by renal biopsy, urinalysis with hematuria/proteinuria, or rising creatinine in the context of a confirmed GPA diagnosis. Clinical validation typically requires necrotizing granulomas on biopsy, PR3-ANCA positivity, and documented glomerulonephritis. If renal involvement is absent or not documented, use M31.30 (without renal involvement) instead.
The distinction between M31.30 and M31.31 is clinically and prognostically significant: renal involvement in GPA carries a higher risk of end-stage renal disease and drives decisions about cyclophosphamide or rituximab induction therapy. Coders should not assign M31.31 based solely on proteinuria or mild urinary abnormalities without explicit physician documentation of renal involvement or glomerulonephritis.
This code sits within the M30–M36 systemic connective tissue disorders block, under the M31 necrotizing vasculopathies category. It is not laterality-dependent and requires no 7th-character extension. When GPA is described as 'NOS' (not otherwise specified), index entries map to M31.30, not M31.31 — renal involvement must be affirmatively stated.
Sibling codes
Other billable codes under M31.3 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 4 cited references ↓
01What is the difference between M31.30 and M31.31?
02Does a mildly elevated creatinine or trace proteinuria justify M31.31?
03Should I code glomerulonephritis separately when M31.31 is assigned?
04Is M31.31 valid as a primary diagnosis on a nephrology claim?
05Does M31.31 require a 7th-character extension?
06How should GPA in remission with chronic kidney disease be coded?
07What CPT codes commonly pair with M31.31 in a rheumatology or nephrology setting?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
Mira AI Scribe
Mira captures the physician's explicit statement of renal involvement, ANCA lab results (PR3/c-ANCA), renal biopsy findings, and current renal function values (creatinine, GFR, urinalysis) from the encounter note to support M31.31. Without that captured documentation, the code defaults to M31.30, understating disease severity and potentially triggering a payer query or downcoded claim.
See how Mira captures M31.31 documentation