PR3ANCA

PR3ANCA, or anti-proteinase 3 antineutrophil cytoplasmic antibodies, are autoantibodies directed against proteinase 3, a serine protease contained within neutrophil azurophilic granules. They are a subset of ANCA and are often detected with a cytoplasmic immunofluorescence pattern (c-ANCA). In clinical practice, PR3-ANCA is most strongly associated with granulomatosis with polyangiitis (GPA, formerly Wegener’s granulomatosis), where a high proportion of patients test positive. PR3-ANCA can also be present in other small-vessel vasculitides, including microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis, but with lower frequency and diagnostic specificity.

The antibodies may contribute to disease by priming and activating neutrophils, promoting degranulation, oxidative burst, and release of inflammatory mediators, leading to necrotizing granulomatous inflammation and vasculitis of small to medium vessels.

Serologic testing uses ELISA to detect antibodies against PR3; results should be interpreted with clinical context. PR3-ANCA positivity increases the likelihood of GPA, though sensitivity and specificity vary, and false positives can occur in infections and inflammatory diseases.

Titers may correlate with disease activity in some patients but are not universally reliable for monitoring. A positive PR3-ANCA result is one element in the diagnostic workup of suspected ANCA-associated vasculitis and is interpreted alongside clinical features and imaging or biopsy when available.