B-074 Comparative Evaluation of Clinical Utility between Indirect Immunofluorescence and Immunoassay Methods for Antineutrophil Cytopalsmic Antibody Detection

Abstract

Listen

Translate article

Abstract Background ANCA testing is essential for the diagnosis of vasculitis, commonly using indirect immunofluorescence(IIF) and immunoassay(IA) methods. Recent guidelines recommend IA as the primary test for suspected GPA and MPA, but actual practice varies among physicians. Here, we retrospectively analyzed ANCA test results, focusing on new cases of ANCA-associated vasculitis, and compared the utility of IIF and IA to guide appropriate test selection. Methods From January 2022 to July 2023, 24 new cases of ANCA-associated vasculitis were diagnosed. We checked whether ANCA testing was performed and the results, and compared the turnaround time(TAT) and costs. IIF ANCA tests were performed on a computer-based automated instrument(Helios), and IA ANCA tests were performed on automated instruments(Alegria, Phadia 250) with MPO antigen and PR3 antigen tested simultaneously in a bundled prescription. Results Among the 24 cases, there were 6 GPA, 7 MPA, 7 EGPA, and 4 ANCA-associated GN, with varying diagnostic sensitivities. GPA and EGPA had different ANCA positivity rates than previously reported, suggesting potential ethnic variations in ANCA expression and positivity rates. The test sequence and results, summarized in Table 1, showed 21 out of 22 cases had identical concordance between methods, with an excellent concordance rate (kappa value=0.83). TAT for IIF was 3,452 minutes, and for IA was 1,491 minutes for the whole period, but IA TAT increased to 2,748 minutes after implementing a days-of-the-week testing system. Test costs, with a relative value score of 118.99 for IIF and 156.05 for IA, indicated IA cost approximately 2.6 times higher, considering the bundled prescription of both antigens for IA ANCA testing. Conclusions Evaluating the utility of both methods for ANCA detection, our study highlights high inter-method agreement in ANCA-associated vasculitis. Considering overall cost and turnaround time, IIF ANCA testing remains effective as a screening test, demonstrating standalone effectiveness.