General information:

ANCA Testing: Anti‑GBM, Anti‑MPO, and Anti‑PR3 – Clinical Significance and Diagnostic Value

Antineurophil - cytoplasmic antibodies (ANCA), Autoimmune vasculitis

Anti‑neutrophil cytoplasmic antibodies (ANCA) are autoantibodies directed against components within neutrophil cytoplasm. They play a central role in diagnosing ANCA‑associated vasculitides, a group of autoimmune diseases that cause inflammation and damage to small blood vessels.

The most clinically relevant ANCA markers include:

• Anti‑GBM (anti–glomerular basement membrane)

• Anti‑MPO (Myeloperoxidase)

• Anti‑PR3 (Proteinase 3)

Quantitative testing of these antibodies is essential for early diagnosis, disease classification, and monitoring treatment response.

What Are ANCA Antibodies?

ANCA antibodies mistakenly target the body’s own cells, leading to inflammation of blood vessels. This can affect multiple organs, most commonly:

• kidneys

• lungs

• skin

• peripheral nerves

• sinuses and upper airways

ANCA‑associated diseases include:

• Granulomatosis with polyangiitis (GPA) – typically linked to anti‑PR3

• Microscopic polyangiitis (MPA) – often associated with anti‑MPO

• Eosinophilic granulomatosis with polyangiitis (EGPA)

• Anti‑GBM disease (Goodpasture syndrome) – a severe condition affecting kidneys and lungs

Types of ANCA Tests

1. Anti‑GBM (Anti–Glomerular Basement Membrane) – Quantitative Test

Anti‑GBM antibodies target the basement membrane of kidney glomeruli and lung alveoli. This test is crucial when evaluating:

• Goodpasture syndrome

• Rapidly progressive glomerulonephritis

• Combined lung and kidney symptoms (e.g., hemoptysis + hematuria)

High anti‑GBM levels indicate a medical emergency requiring immediate treatment.

2. Anti‑MPO (Myeloperoxidase) – Quantitative Test

Anti‑MPO antibodies are characteristic of:

• Microscopic polyangiitis (MPA)

• Eosinophilic granulomatosis with polyangiitis (EGPA)

• Some cases of necrotizing glomerulonephritis

Elevated anti‑MPO levels may also appear in:

• chronic infections

• autoimmune disorders

• inflammatory bowel disease

3. Anti‑PR3 (Proteinase 3) – Quantitative Test

Anti‑PR3 antibodies are strongly associated with:

• Granulomatosis with polyangiitis (GPA)

• Vasculitis involving the lungs and upper airways

• Relapsing forms of ANCA‑associated vasculitis

This test is valuable for both initial diagnosis and monitoring disease activity.

When Is ANCA Testing Recommended?

A physician may order an ANCA test when symptoms suggest systemic vasculitis, such as:

• unexplained kidney dysfunction

• blood in urine

• pulmonary hemorrhage

• chronic sinusitis or nasal polyps

• skin purpura

• systemic symptoms: fever, weight loss, fatigue

Benefits of Quantitative ANCA Testing

• High diagnostic accuracy

• Monitoring treatment response

• Predicting risk of relapse

• Differentiating between types of vasculitis

Sample required:

Venous blood

Key words:

Antineurophil - cytoplasmic antibodies