ANCA Testing — SCE Rheumatology MCQ

Correct answer: E — Myeloperoxidase (MPO)

The correct answer is E, myeloperoxidase. In ANCA-associated vasculitis, a perinuclear fluorescence pattern on ethanol-fixed neutrophils is most commonly associated with MPO-ANCA. By contrast, PR3-ANCA most often produces a cytoplasmic ANCA pattern. Elastase, lactoferrin and bactericidal/permeability-increasing protein can also produce perinuclear or atypical ANCA patterns, but these specificities are less common and are often encountered outside classic ANCA-associated vasculitis. The fluorescence pattern does not establish antigen specificity: contemporary testing identifies PR3-ANCA and MPO-ANCA using antigen-specific immunoassays. High-quality immunoassays may be used as primary tests, so indirect immunofluorescence does not invariably need to precede or be confirmed by ELISA.

Reference: Radice A, Sinico RA. Antineutrophil cytoplasmic antibodies (ANCA). Autoimmunity. 2005;38(1):93–103. https://pubmed.ncbi.nlm.nih.gov/28905856/