Spectrum of ANCA-Associated Disorders According to Serological Phenotype in Routine Care: Retrospective Case Series of 209 Patients

Abstract

Objective : To summarize the experience of three years of positive ANCA (anti-neutrophil cytoplasmic antibodies) testing in a single university based hospital. We describe the clinical features according to ANCA phenotype of patients who did and did not have ANCA- associated vasculitis (AAV). Methods : We did a review of all samples tested for ANCA in a 3 year-period (2005-2007). Each sample was tested by indirect immunofluorescence (IIF) and enzyme-linked-immunosorbent assay (ELISA). Sera were considered as positive for ANCA testing if either IIF or ELISA for MPO or PR3 antigen specificity was positive. Patients were considered as having AAV on established diagnostic criteria and algorithms. Results : The positive ANCA population consisted in 209 patients, 54 were classified in the AAV group and 155 patients constituted the “Others” group. The typically most relevant ANCA phenotypes (C-ANCA/anti-PR3+ and P-ANCA/anti-MPO+) were detected in 90 % (49/54) of patients in the AAV group and only 10% (15/155) of the “Others” group (p < 0.001). Among the latter none developed AAV during follow-up. Positive IIF alone was found in 4% (2/54) of the AAV group and in 68% (105/155) of the “Others” group (p < 0.001). In patients without AAV, positive IIF alone or positive ELISA with negative IIF represented the main ANCA pattern. Conclusion : In routine clinical practice, most patients with positive ANCA testing do not have AAV. The typical ANCA pattern (C-ANCA/anti-PR3+ or P-ANCA/anti-MPO+) remains a strong predictor of AAV in patients with a high level of suspicion for systemic vasculitis. In other cases, ANCA positivity should be interpreted with extreme caution.