False positive antineutrophil cytoplasmic antibody in a patient with infective endocarditis

An unusual cause for fever of unknown origin in a patient with a prosthetic valve

“…The presence of high-titre ANCA (anti-proteinase 3 specific) in the setting of a high index of suspicion for vasculitis is sufficient for diagnosis, even in the absence of tissue confirmation 7. Although false positive c-ANCA titres in patients with subacute bacterial endocarditis is known, the titres are usually weakly positive and a positive titre by ELISA and IF is 73% sensitive and 99% specific for Wegener granulomatosis 8. The possibility of infective endocarditis was ruled out as the patient did not satisfy the Duke criteria and no clinical improvement was noticed when she was treated for a significant duration with the aforementioned antibiotics.…”