What this test measures
Anti-PR3 (proteinase 3) antibodies target a serine protease in neutrophil azurophilic granules. On indirect immunofluorescence of ethanol-fixed neutrophils these antibodies produce a diffuse cytoplasmic pattern (c-ANCA). Confirmation is by quantitative PR3-specific ELISA.
PR3-ANCA is one of two main pathogenic ANCA antibodies. Together with MPO-ANCA, they define ANCA-associated vasculitis (AAV) — small-vessel vasculitides that affect kidneys, lungs, upper airway, skin and peripheral nerves.
Why it matters
PR3-ANCA is the dominant serological marker of granulomatosis with polyangiitis (GPA, formerly called Wegener granulomatosis) — present in 80–90% of patients with generalised disease. GPA causes a characteristic triad of upper respiratory (chronic sinusitis, saddle-nose deformity, subglottic stenosis), lower respiratory (pulmonary nodules, cavities, haemorrhage), and renal (rapidly progressive glomerulonephritis) involvement. PR3-ANCA also appears in a smaller proportion of microscopic polyangiitis and EGPA patients.
In Indian rheumatology practice, PR3-ANCA is essential in workup of unexplained chronic sinusitis or saddle-nose deformity in adults, lung nodules with cavitation, rapidly progressive kidney disease, peripheral neuropathy with systemic features, and palpable purpura. Early diagnosis and treatment (cyclophosphamide or rituximab + steroids) dramatically reduces mortality in what was once a uniformly fatal disease. PR3-ANCA positive disease tends to relapse more often than MPO-ANCA disease, making long-term monitoring important.
How to prepare
No fasting required. Continue all medications. Mention any immunosuppressants you are taking and the indication — they may lower titre but rarely give a false-negative.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| PR3-ANCA IgG (U/mL)[1][2][3] | Negative: < 20 U/mL (assay-dependent) | Negative makes GPA less likely but does not rule it out — a small proportion are ANCA-negative ("seronegative AAV"). Some MPA and EGPA patients are MPO-positive instead. | Positive PR3-ANCA strongly supports GPA. Higher titres correlate with active disease; rising titres can predict relapse and may guide preemptive treatment adjustment. Drug-induced PR3-ANCA is less common than MPO-induced. |
ANCA-associated vasculitis — clinical features
| Feature | GPA (PR3-dominant) | MPA (MPO-dominant) | EGPA |
|---|---|---|---|
| ENT (sinusitis, saddle nose) | Very common | Less common | Rare |
| Lung disease | Nodules, cavities, haemorrhage | Haemorrhage, fibrosis | Asthma, infiltrates |
| Kidney disease | Common | Very common | Less common |
| Asthma + eosinophilia | Rare | Rare | Defining feature |
| Predominant ANCA | PR3-ANCA (~80%) | MPO-ANCA (~60%) | MPO-ANCA (~40%) |
| Relapse rate | High (~50%) | Lower (~30%) | Variable |
Frequently asked questions
Do I need fasting?
No fasting required.
What does c-ANCA pattern mean?
On immunofluorescence of neutrophils, antibodies produce a diffuse cytoplasmic staining pattern (c-ANCA). This is confirmed as PR3-ANCA by ELISA. The combination is highly specific for GPA.
Positive PR3-ANCA — is GPA confirmed?
Strongly supports it in the right clinical context. Diagnosis usually requires biopsy (kidney, lung, sinus) showing characteristic granulomatous vasculitis.
Does treatment lower the titre?
Yes. Effective induction (cyclophosphamide or rituximab + steroids) usually reduces titre. Rising titre in a previously controlled patient may predict relapse.
Are PR3 and MPO both tested?
Yes — modern AAV panels test both because patients can be positive for either, and the choice of induction therapy may differ slightly.
How long does the report take?
Typically 2–4 days.
Will rituximab work in PR3-ANCA disease?
Yes — rituximab is at least as effective as cyclophosphamide for inducing remission and is preferred for relapsing PR3-ANCA disease.
Related Autoimmune / Rheumatology tests
Tests commonly ordered alongside PR3 - ANCA ( C-ANCA ), or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — ANCA Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Granulomatosis with Polyangiitis · accessed 2026-05-30T00:00:00.000Z
- ACR/Vasculitis Foundation — AAV Guideline · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — PR3 Antibody · accessed 2026-05-30T00:00:00.000Z
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