Bacterial endocarditis associated with proteinase 3 anti-neutrophil cytoplasm antibody

Anti-neutrophil cytoplasm antibodies (ANCA) are useful diagnostic markers in a range of small vessel vasculitides. While non-specific ANCA have been reported in association with a variety of autoimmune, haematological and infectious conditions, the combination of a cytoplasmic staining pattern on indirect immunofluorescence (IIF) of human neutrophils, with antibodies specific for proteinase 3 (PR3) by enzyme-linked immunosorbent assay (ELISA), is reported to be 99% specific for Wegener’s granulomatosis versus disease controls [1]. This serological finding in association with other diseases that manifest vasculitic phenomena can therefore result in diagnostic uncertainty and erroneous treatment decisions. We report three cases of bacterial endocarditis in association with PR3-ANCA and discuss the implications for diagnosis and management.