Background Antineutrophil cytoplasmic antibodies (ANCA) are autoantibodies directed against constituents of primary granules of neutrophils. ANCA are the serological marker of some idiopathic systemic vasculitides, predominantly involving small and medium-sized blood vessels, such as granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), which are known as the ANCA-associated vasculitis (AAV). Although ANCA are the serological hallmark of AAV, ANCA have been reported in a number of other conditions including infections, malignancies, connective-tissue diseases, liver and gastrointestinal diseases, renal diseases, and other vasculitides. Many studies have evaluated the clinical value of ANCA testing, but few analyze ANCA utility under actual routine conditions in unselected patients with the usual laboratory techniques.
Objectives Our aim was to evaluate the positive predictive value (PPV) of ANCA testing in a cohort of unselected patients from a Spanish tertiary hospital.
Methods We reviewed the clinical charts of patients with positive ANCA testing between January 2014 and December 2014 at the Immunology Department from a 1.000-bed tertiary teaching hospital from Barcelona (Spain). Detection methods included indirect immunofluorescence (IIF) for all testing request and chemiluminescent immuno-assay (CLIA) for antibodies against mieloperoxidase (MPO) and proteinase 3 (PR3) in patients with positive IIF.
Results Out of 1615 patients with ANCA testing request, 298 (18.5%) tested positive. Atypical pattern (X-ANCA) was the most frequent (50.3%) over perinuclear pattern (P-ANCA) (27.5%) and cytoplasmatic pattern (C-ANCA) (22.1%). 35.4% of P-ANCA and 36.4% of C-ANCA were positive for MPO-ANCA and PR3-ANCA, respectively, whereas 97.3% of X-ANCA tested negative by CLIA. 53 (18.2%) patients with positive ANCA had a diagnosis of ANCA-associated vasculitis (AAV). Other diagnosis were the following: 26 (8.9%) connective tissue diseases, 13 (4.5%) vasculitides non-AAV, 13 (4.5%) autoimmune liver diseases and 11 (3.8%) inflammatory bowel disease. The combination of IIF and CLIA showed the best diagnostic accuracy. P-ANCA with anti-MPO had a PPV of 75% for AAV, and PPV of C-ANCA with anti-PR3 was 70.8% for GPA.
Conclusions This study proves that ANCA testing with modern commonly commercially available methods has an elevated PPV for AAV in routine clinical practice.
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Disclosure of Interest None declared