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Objectives Anti-dsDNA antibodies are a hallmark of systemic lupus erythematosus (SLE) and are widely used for diagnosis and disease monitoring. However, discrepancies between screening ELISA assays and confirmatory Crithidia luciliae immunofluorescence (CLIF) tests remain a challenge in clinical practice, potentially leading to false-positive and false-negative interpretations. This study examines the longitudinal correlation between dsDNA ELISA and CLIF assays in SLE patients.Methods We retrospectively identified 313 patients between April 2015 and April 2024. Applying concordance criteria requiring both assays to be performed within a ±2-week window further reduced the cohort to 184 patients, who were included in the final analysis. Anti-dsDNA was assessed by ELISA and confirmed with CLIF. Patients were categorized into four groups based on assay results: Y/Y (positive by both), Y/N (positive ELISA only), N/Y (positive CLIF only), and N/N (negative by both). Comparisons were performed at baseline and follow-up intervals over 36 months. Statistical significance was set at p < 0.01.Results At baseline (n=184), 23% of patients were classified as true positives (Y/Y: positive by both ELISA and CLIF) and 40% as true negatives (N/N: negative by both). Over time, the proportion of true positives significantly increased, reaching 29% at 24 months (p=0.0023) and 35% at 36 months (p=0.0008). In contrast, true negatives steadily decreased, particularly beyond 24 months, as patients converted to either Y/Y or Y/N groups. ELISA-only positives (Y/N), representing potential false positives, consistently accounted for a substantial proportion of patients (29–44%) across all time points. Conversely, CLIF-only positives (N/Y), representing potential false negatives, were infrequent (1–5%) but not negligible. Overall, concordance between ELISA and CLIF fluctuated across follow-up, with the strongest alignment observed at baseline, 24 months, and 36 months.Abstract PO:02:061 Figure 1Conclusions In this real-world SLE cohort, ELISA-only positives remained consistently common, highlighting the potential for overestimation of activity when relying solely on ELISA. Conversely, CLIF-only positives were rare but present, emphasizing that ELISA may occasionally miss clinically relevant antibodies. These findings underscore the complementary value of dual testing to provide a more reliable assessment of anti-dsDNA status and improve the accuracy of disease activity evaluation in longitudinal SLE management.