058. ANTINEUTROPHIL CITOPLASMIC ANTIBODIES IN THE REAL WORLD: RESULTS: FROM A SURVEY IN A GENERAL LABORATORY

Abstract

Background: Antineutrophil cytoplasmic antibodies (ANCA) are biomarkers of small-vessels vasculitis known as ANCA-associated vasculitis, but they are also diagnostic tools for other diseases such as ulcerative colitis, primary sclerosing cholangitis and type I autoimmune hepatitis. This study aims to evaluate the profile of ANCA tests performed in a national-wide general laboratory. Method(s): A cross- sectional observational study was performed and information about all ANCA tests performed in a 23-month period was analyzed. Positivity, titer and patterns of ANCA were checked for indirect immunofluorescence (IIF) results specificity was detected by enzyme-li Co ked immunoassay (ELISA) for anti-proteinase 3 (anti-PR3) and anti-myeloperoxidase (anti-MPO) antibodies. Result(s): 8,144 ANCA tests were performed by IIF and 5.3% of them were positive (i.e. titers > 1/40), around 70% of ANCA tests were between 1/20 and 1/80, whereas less than 10% of positive IIF ANCA tests had titers > 1/640. Atypical ANCA (A-ANCA) was the most frequent pattern (47.5%) followed by cytoplasmic ANCA (C-ANCA) (32.4%), perinuclear ANCA (P-ANCA) (17.6%) and atypical C-ANCA (2.3%). P-ANCA positive sera had significantly higher median titers than C-ANCA (p < 0.0001) and higher than A-ANCA (p = 0.001) positive sera. The median A-ANCA titers were even higher than titers of C-ANCA positive sera (p = 0.001). Anti- MPO antibodies were detected in 42.0% of positive P-ANCA tests while only 32.6% out of the C-ANCA positive sera were positive for anti-PR3 antibodies. Patients presenting positive anti-PR3 and anti-MPO antibodies had significantly higher C-ANCA and P-ANCA median titers, respectively. Among positive A- ANCA and C-ANCA results the specialties that most frequently ordered these tests were gastroenterologists and rheumatologists, whereas among positive P-ANCA results the most frequent specialties were nephrologists followed by rheumatologists. Conclusion(s): In a national-wide general laboratory, the positivity of ANCA tests by IIF is infrequent at low titers. Positive results for anti-PR3 and anti-MPO are observed in less than half of patients with positive C-ANCA and P-ANCA, respectively, and this was significantly associated with ANCA titers. The low frequency of positive tests may be due to different specialists ordering ANCA in a low pretest probability scenario.