Antibodies against double-stranded DNA are key biomarkers used in the diagnosis, monitoring of disease activity and prediction of flares in systemic lupus erythematosus. In addition to high avidity IgG antibodies, which are strongly correlated with disease activity, patients may also present antibodies of varying isotypes and avidities. The absence of standardized reference material, combined with variability among available detection methods, presents a significant challenge to the standardization of anti-dsDNA antibody testing. For compehensive serological evaluation, the use of two different detection methods is recommended. A comprehensive understanding of the analytical characteristics and limitations of each method is crucial for accurate interpretation of the results. The Immunology Laboratory at the Clinical Department of Rheumatology, University Medical Centre Ljubljana, has been using indirect immunofluorescence method on Crithidia luciliae cells as the initial method for determining antibodies against double-stranded DNA for a decade, with positive results confirmed by an in-house validated Farr-FIA method.
In this study, the performance of a next-generation chemiluminescent immunoassay was assessed in comparison with routine immunochemical methods. A positive result obtained by this assay initiates testing with a second-tier method, which serves as the entry point of the standard diagnostic algorithm. The chemiluminescent immunoasssay demonstrated good repeatability and intermediate precision at two concentration levels, with coefficients of variation ranging from 3.5% to 4.2%, in line with expected analytical performance criteria. Regression analysis yielded a slope of 1.018 (95% CI: 0.828–1.045), indicating consistency with the manufacturer’s linear model. The method showed strong correlation with the Farr-FIA (Spearman’s rho = 0.71), supporting its clinical relevance. Among 192 tested samples, the chemiluminescent immunoasssay showed high agreement with indirect immunofluorescence assays from different manufacturers (Cohen’s kappa = 0.83) and the diagnostic algorithm achieved an overall agreement of 89.1%. The method was able to detect additional patients with dsDNA antibodies due to its broader avidity range; however, it failed to identify some SLE cases that were confirmed by the established diagnostic algorithm. In conclusion, although the evaluated two-step algorithm incorporating CLIA technology demonstrated diagnostic value, it did not outperform the established routine approach. These findings underscore the critical importance of method selection and algorithm design in ensuring reliable serological assessment for SLE diagnostics.
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