RESUMO
BACKGROUND: Antibodies against neutrophil cytoplasm (ANCA) are associated with vasculitis. There are different methods to determine their presence. The interference of antinuclear antibodies (ANA) in the differentiation between P-ANCA and C-ANCA patterns has been described. OBJECTIVE: To determine the frequency of ANCA in a population with manifestations of autoimmune disease, and evaluate the interference of ANA in its interpretation. MATERIALS AND METHODS: Retrospective, descriptive nonexperimental cross-sectional study, including 3,330 data. The presumptive diagnosis was autoimmune disease and a test for ANCA was requested. The ANCA and ANA determinations were made by indirect immunofluorescence, L-ANCA® and CytoBead® ANCA. Anti-proteinase 3 and anti-myeloperoxidase were detected by ELISA and CytoBead® ANCA. RESULTS: ANCAs were positive in 10.21% and 12.64% of those positive for ANCA were positive for ANA. The inter-rater agreement statistic (Kappa) for anti-PR3 between CytoBead ANCA and ELISA was 100% (K=1.00; P<.05) and the agreement between anti- myeloperoxidase by ELISA and CytoBead® ANCA was high (K=0.94; P<.05). 30% of those with ANCAs had a diagnosis of a type of vasculitis; 20% of them had an autoimmune disease. CONCLUSIONS: The results suggest an overestimated request for ANCAs as a diagnostic aid in primary care which was not addressed. For an adequate evaluation of ANCAs, the indirect immunofluorescence technique should be implemented for the control and confirmation with the determination of specific antigens for anti- proteinase 3 and anti- myeloperoxidase in any of the confirmatory assays. The high concordance shown by ANCA CytoBeads makes us consider the use of this alternative for the determination of ANCAs and the confirmation. Given the interference of ANAs, the ANA test by IFI in the presence of positive P-ANCA results is recommended in order to minimize "false positives".