What is the indication for p-ANCA (perinuclear anti-neutrophil cytoplasmic antibodies) and c-ANCA (cytoplasmic anti-neutrophil cytoplasmic antibodies) in diagnosing vasculopathy (arteriopathy)?

From the Guidelines

ANCA testing, including p-ANCA and c-ANCA, is crucial for diagnosing vasculopathy, specifically ANCA-associated vasculitides, when patients present with clinical features suggestive of small vessel vasculitis, such as unexplained renal dysfunction, pulmonary hemorrhage, or chronic sinusitis, as indicated by the 2021 American College of Rheumatology/Vasculitis Foundation guideline 1.

Indications for p-ANCA and c-ANCA Testing

The primary indication for p-ANCA and c-ANCA testing is to diagnose and differentiate between various forms of ANCA-associated vasculitides, including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA) 1.

• p-ANCA typically targets myeloperoxidase (MPO) and is associated with MPA and EGPA.
• c-ANCA usually targets proteinase 3 (PR3) and is characteristic of GPA.

Clinical Context and Interpretation

It is essential to interpret ANCA test results in the clinical context, considering the patient's symptoms and medical history, as the sensitivity and specificity of ANCA testing vary by disease subtype 1.

• Negative results do not exclude vasculitis if clinical suspicion remains high.
• Early testing is crucial to allow for timely initiation of immunosuppressive therapy, which can prevent irreversible organ damage.

Treatment and Management

The 2021 American College of Rheumatology/Vasculitis Foundation guideline provides evidence-based recommendations for the treatment and management of ANCA-associated vasculitides, including the use of high-dose corticosteroids, cyclophosphamide, and rituximab 1, 2.

• Prompt diagnosis and treatment can significantly improve patient outcomes and reduce morbidity and mortality.

From the Research

Indications for p-ANCA and c-ANCA in Diagnosing Vasculopathy

• p-ANCA (perinuclear anti-neutrophil cytoplasmic antibodies) and c-ANCA (cytoplasmic anti-neutrophil cytoplasmic antibodies) are used in the diagnosis of ANCA-associated vasculitis (AAV) 3, 4, 5, 6, 7
• The presence of p-ANCA is often associated with microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), while c-ANCA is commonly found in granulomatosis with polyangiitis (GPA) 4, 6
• p-ANCA is typically associated with anti-myeloperoxidase (MPO) antibodies, whereas c-ANCA is associated with anti-proteinase 3 (PR3) antibodies 4, 5, 6, 7
• The combination of indirect immunofluorescence test (IIFT) and line immunoassay (LIA) is considered an optimal testing strategy for the laboratory diagnosis of AAV 4
• High-quality immunoassays can be used as the primary screening method for patients suspected of having AAV, without the need for IIFT 5

Clinical Associations

• c-ANCA is detected in 77.8% of AAV patients, while p-ANCA is detected in 22.2% 6
• In GPA, c-ANCA is detected in 80.9% and p-ANCA in 17.4%, while in MPA, c-ANCA is detected in 50% and p-ANCA in 50% 6
• The pattern of ANCA positivity can vary depending on the specific type of AAV and the population being studied 6, 7

Diagnostic Approaches

• The diagnosis of AAV involves a combination of clinical evaluation, laboratory testing, and imaging studies 3, 4, 5, 6, 7
• The use of ANCA testing, including p-ANCA and c-ANCA, is an important component of the diagnostic approach for AAV 3, 4, 5, 6, 7