What is the significance in routine care of c-ANCA/PR3-ANCA in the absence of systemic vasculitis? A case series.

OBJECTIVE ANCA has come to play an important role in diagnosing vasculitis. In selected populations c-ANCA/PR3-ANCA has a high specificity and sensitivity for vasculitis. In clinical practice, how individuals with c-ANCA/PR3-ANCA but without sufficient evidence of systemic vasculitis should be managed is unclear. We therefore retrospectively assessed the disease panorama and outcome in a consecutive series of individuals with c-ANCA/PR3-ANCA, and studied in detail those individuals who turned out not to fulfil criteria for vasculitic disease. METHODS The study population consisted of 74 consecutive patients who all had a positive test for C-ANCA and PR3-ANCA between 1992 and 2002 at the Immunology laboratory at Uppsala University Hospital, Sweden. The patients' medical files were reviewed and their diagnosis re-evaluated through June 2006. RESULTS 18 of the 74 ANCA-positive individuals did not present clinical evidence supportive of, or insufficient to support, a diagnosis of systemic vasculitis, but presented a range of other diseases. During a mean follow-up of 6.8 years, none of these 18 patients developed vasculitis. CONCLUSIONS Individuals with a positive c-ANCA and PR3-ANCA but no vasculitis at the time of testing run an unknown but likely small risk of later developing vasculitis. In this group, a positive ANCA may represent background noise (borderline titres) or be a marker of inflammatory activity rather than of vasculitic disease (high titres).