The indirect immunofluorescence (IIF) technique for antineutrophil cytoplasmic antibodies (ANCA) detection is subject to substantial differences across laboratories. This study aimed to assess the impact of improvements in the IIF-ANCA technique on the positivity rate of ANCA tests. A cross-sectional study was performed with serum samples from patients with ANCAassociated vasculitis (AAV), autoimmune hepatitis (AIH), and ulcerative colitis (UC). A paired analysis was performed for IIFANCA results using the traditional method and a modified protocol after a series of specific adjustments in the technique based on the protocol of IIF-ANCA test performed at a nation-wide private laboratory in Brazil. ANCA specificity was assessed by ELISA for anti-proteinase 3 (PR3) and anti-myeloperoxidase (MPO) antibodies. Sixty-one patients were evaluated. The positivity rate of IIF-ANCA tests at disease presentation performed at the University reference laboratory was 32.3% in AAV, AIH, and UC patients, whereas the positivity rates of IIF-ANCA and ELISA tests in other laboratories were 75.0 and 72.7%, respectively. After modifications in the IIF-ANCA technique, there was a significant increase in the positivity rate (14.8 vs 34.3%; P=0.0002) and in median titers [1/40 (1/30–1/160) vs 1/80 (1/40–1/80); P=0.0003] in AAV, AIH, and UC patients. UC had the highest increment in positive results from 5.3 to 36.8%. There was poor agreement between MPO-or PR3-ANCA and both IIF-ANCA techniques. In conclusion, modifications in the IIF-ANCA protocol led to a significant improvement in its positivity rate and titers.
CITATION STYLE
Zarur, E. B., Rodrigues, S. H., Ambrogini, O., Ferraz, M. L. G., Mastroianni-Kirsztajn, G., Andrade, L. E. C., & Souza, A. W. S. (2023). Improvement of indirect immunofluorescence technique to detect antineutrophil cytoplasmic antibodies and its impact on test positivity rate. Brazilian Journal of Medical and Biological Research, 56. https://doi.org/10.1590/1414-431X2023e12636
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