Analytical and clinical comparison of two fully automated immunoassay systems for the detection of autoantibodies to extractable nuclear antigens

Background Detection of antinuclear antibodies (ANA) by indirect immunofluorescence assay (IIFA) is increasingly substituted by fully automated solid phase immunoassays. This study evaluated the performance of an automated chemiluminescence immunoassay (CIA) and fluorescence enzyme immunoassay (FEIA) and compared their performance to that of IIFA. Methods The study included an unselected prospective study population suspected of systemic autoimmune rheumatic disease. ANA were measured by IIFA, while in parallel sera were tested by CIA QUANTA Flash CTD Screen Plus on the BIO-FLASH® and FEIA EliA CTD Screen on the Phadia® 250 system. As validation, retrospective cohorts of patients with ANA-associated rheumatic disease (AARD) and healthy controls were tested. Results Prospectively, sensitivity of IIFA, CIA and FEIA was 90%, 99% and 92%, respectively. Specificity was 76%, 76% and 84%, respectively. Total percent agreements between the three methods were 75.2% (IIFA vs. CIA), 79.2% (IIFA vs. FEIA) and 85.4% (FEIA vs. CIA). The AUC values were 0.95 for CIA and 0.93 for FEIA and did not significantly differ. Retrospectively in individual AARD cohorts, similar results were obtained comparing both CTD screens. Conclusions Both FEIA and CIA CTD screen significantly outperformed IIFA, with a higher specificity for FEIA and higher sensitivity for CIA. Based on ROC analysis, major contributor to the difference between the two solid phase immunoassays was the cut-off.

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