Diagnostic Performance of Anti-dsDNA Tests by Indirect Immunofluorescence and Enzyme-linked Immunosorbent Assay in Patients with Systemic Lupus Erythematosus.

Background: Several laboratory techniques for anti double-stranded (ds) DNA detection in systemic lupus erythematosus (SLE) are available, with variable diagnostic performance. We aimed to evaluate anti-dsDNA's diagnostic performance by indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (EIA).
Methods: We conducted a single-center retrospective (2015 to 2020) study. Patients with anti-dsDNA tests by IIF and EIA were included. We evaluated the indications, applications, concordance, positive predictive value (PPV) of anti-dsDNA to confirm SLE diagnosis or flares, and associations of disease manifestations with positivity with each technique.
Results: A total of 1368 reports of anti-dsDNA tests by IIF and EIA and the corresponding medical records of the patients were analyzed. The main indication for anti-dsDNA testing was to help in the diagnosis of SLE in 890 (65%) of the samples, and the main application after obtaining the results was SLE exclusion in 782 (57.2%) cases. The combination with the highest frequency was the negativity result by both techniques in 801 (58.5%) cases (Cohen kappa 0.57). Both methods were positive in 300 patients with SLE (Cohen kappa 0.42). The PPVs of anti-dsDNA tests to confirm diagnosis/flare was 79.64% (95% CI, 75.35-83.35) by EIA, 78.75% (95% CI, 74.27-82.62) by IIF, and 82% (95% CI, 77.26-85.93) when both were positive.
Conclusions: Anti-dsDNA detection by IIF and EIA are complementary and may indicate different clinical patterns in patients with SLE. The detection of anti-dsDNA antibodies by both techniques has a higher PPV than either separately for confirming SLE diagnosis or flares. These results highlight the need for evaluating both methods in clinical practice.
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