Proteinase 3 Antibodies

What is the Proteinase 3 Antibodies test?

The Proteinase 3 Antibodies test measures antibodies directed against proteinase 3 (PR3), an enzyme found in neutrophils. These antibodies are a type of ANCA (anti-neutrophil cytoplasmic antibodies) and are strongly associated with certain autoimmune vasculitic conditions.

PR3-ANCA is most commonly linked to granulomatosis with polyangiitis (GPA), a form of small-vessel vasculitis that can affect the lungs, kidneys, sinuses, and other organs.

This blood test is used to support diagnosis, assess disease activity, and help differentiate between types of vasculitis and autoimmune inflammation.

Why do I need a test for Proteinase 3 Antibodies?

ANCA-associated vasculitis can cause serious organ damage if not identified early. Symptoms are often non-specific and may involve multiple organ systems, making targeted antibody testing essential.

This test is particularly useful when inflammatory symptoms involve the kidneys, lungs, ENT system, or blood vessels.

You may benefit from this test if you experience:

• Persistent sinus or nasal inflammation

• Unexplained kidney abnormalities

• Blood or protein in urine

• Chronic cough or breathlessness

• Lung infiltrates on imaging

• Unexplained fatigue and weight loss

• Joint or muscle pain with inflammation

• Suspected autoimmune or vasculitic disease

Benefits of the Proteinase 3 Antibodies test

1. Supports vasculitis diagnosis
   Strongly associated with ANCA-related vasculitis.

2. Helps identify granulomatosis with polyangiitis
   A key marker in GPA assessment.

3. Assesses autoimmune inflammation
   Reflects immune-mediated vessel injury.

4. Supports early detection of organ involvement
   Important for kidney and lung protection.

5. Helps differentiate autoimmune conditions
   Distinguishes PR3-ANCA from other ANCA subtypes.

6. Useful for disease monitoring
   Levels may reflect disease activity in some patients.

7. Guides further specialist investigation
   Supports referral to rheumatology or nephrology.

8. Non-invasive autoimmune assessment
   Requires only a blood sample.

Step-by-step – how we offer Proteinase 3 Antibodies testing

Clinic-based testing (UK-wide)

• Choose your nearest UK clinic

• Attend your appointment

• Blood sample collected by a qualified clinician or phlebotomist

• Sample is sent to the laboratory for analysis

At-home or hotel testing (+£60)

• A qualified phlebotomist visits your home or hotel

• Blood sample collected in a comfortable, familiar setting

• No clinic visit or travel required

Both services are available UK-wide.

Your Proteinase 3 Antibodies results explained

Negative PR3 antibodies

Negative results suggest no detectable PR3-ANCA at the time of testing. This makes PR3-associated vasculitis less likely, though it does not completely exclude autoimmune disease.

Clinical correlation with symptoms and other tests is important.

UK reference interpretation:

• Negative: Not detected

Low-positive PR3 antibodies

Low-level positivity may be seen in early disease, mild autoimmune activity, or non-specific immune activation. Results should be interpreted cautiously and alongside clinical findings.

Repeat or additional testing may be advised.

UK reference interpretation:

• Low positive: Above reference threshold

High PR3 antibodies

High PR3 antibody levels are strongly associated with active ANCA-associated vasculitis, particularly granulomatosis with polyangiitis. Elevated levels may correlate with disease activity.

Prompt specialist evaluation is often required.

UK reference interpretation:

• High positive: Significantly above reference range