What is the significance of neutrophil staining with atypical Anti-Neutrophil Cytoplasmic Antibodies (ANCA)?

From the Guidelines

Atypical ANCA staining patterns, including those with neutrophil staining, are generally considered less specific for systemic vasculitides and may require additional testing for diagnostic clarity. When considering the clinical significance of atypical ANCA patterns, it's essential to understand that these patterns may not fit the classic cytoplasmic (c-ANCA) or perinuclear (p-ANCA) patterns, which are more commonly associated with specific vasculitides, such as granulomatosis with polyangiitis (c-ANCA) or microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis (p-ANCA) 1. The detection of atypical ANCA patterns may be seen in various conditions, including inflammatory bowel disease, autoimmune hepatitis, rheumatoid arthritis, or drug-induced autoimmunity. Given the limited diagnostic value of atypical ANCA patterns alone, specific antigen testing, such as anti-PR3 or anti-MPO ELISAs, should be performed to clarify the clinical significance. Key points to consider in the interpretation of atypical ANCA staining include:

• The pattern of staining may not be specific to a particular vasculitis or disease process
• Additional testing, such as specific antigen assays, is necessary to determine the clinical relevance of the atypical ANCA pattern
• The presence of atypical ANCA may be associated with a range of conditions, and clinical correlation is essential for accurate diagnosis and management. In the context of eosinophilic granulomatosis with polyangiitis (EGPA), ANCA positivity, typically against myeloperoxidase (MPO), is detectable in approximately 40% of cases and is associated with a different frequency of clinical manifestations 1. However, the atypical ANCA pattern itself does not provide sufficient information for a definitive diagnosis, and a comprehensive diagnostic approach, including clinical evaluation, laboratory testing, and histopathological examination, is necessary to establish a diagnosis and guide management.

From the Research

Neutrophil Staining and Atypical ANCA

• Neutrophil staining patterns can be used to diagnose and monitor ANCA-associated vasculitis 2, 3
• Indirect immunofluorescence on ethanol-fixed neutrophils can recognize two major fluoroscopic patterns: a diffuse cytoplasmic staining (C-ANCA) and a perinuclear/nuclear staining (P-ANCA) 2
• Atypical ANCA patterns can be seen in various conditions, including inflammatory bowel diseases, other autoimmune diseases, and infections 2
• The clinical significance of atypical ANCA patterns is unclear, and their presence should be interpreted with caution 2, 4

ANCA Testing and Interpretation

• ANCA testing is a cornerstone immunoassay in the management of ANCA-associated vasculitis 4
• The International Consensus Statement for Testing and Reporting ANCA recommends that all sera are screened for ANCA by indirect immunofluorescence and that IIF-positivity is confirmed by direct ELISAs 3
• Automated ANCA testing by computer-aided microscopic evaluation can be a reliable alternative to classical microscopic evaluation, but requires correction by trained personnel during on-screen validation 5

Neutrophil Activation and Autoimmune Diseases

• Neutrophils play a significant role in the pathogenesis of autoimmune diseases, including rheumatoid arthritis 6
• Neutrophil extracellular traps (NETs) may play a pathogenic role in rheumatoid arthritis and could be a source of autoantigens 6
• The determination of NETs in peripheral blood may be a useful biomarker of disease activity in rheumatoid arthritis and other immune-mediated diseases 6