P12 Sensitivity differences in ELISA versus EliA for detecting anti-dsDNA antibodies: awareness for the clinician

Objective Heterogeneity among clinical presentation can cause difficulties when diagnosing SLE. One of the most specific immunologic criteria for this disease are anti-dsDNA antibodies. However, to detect these autoantibodies, different test methods are offered. This study will compare sensitivity of ELISA and EliA by synchronous testing in SLE patients. Methods Between March and August 2022 samples from (suspected) SLE patients, undergoing anti-dsDNA testing, were simultaneously measured by dsDNA/nucleosome ELISA (positive IU/ml >100) and dsDNA EliA (positive > 15 IU/ml). SLICC 2012 classification criteria were used to include SLE patients. Clinical data including clinical SLEDAI-2K were retrospectively retrieved from medical records. Results Out of 163 tested patients, 143 SLE patients were eligible for study analysis. Demographic characteristics are summarized in table 1. Sensitivity was 88.4% for ELISA versus 63.0% in EliA (McNemar. p), ELISA had been positive in the past. Median SLEDAI was higher for patients with EliA-/ELISA+ discrepancy (see table 2). Conclusions In our SLE cohort, there was a striking difference in sensitivity between anti-dsDNA test results (mainly EliA-/ELISA+ discrepancy) despite active disease in these patients. We hypothesize that this might be explained by the presence of anti-nucleosome antibodies, which can be detected by dsDNA/nucleosome ELISA or ENA-immunoblot. Clinicians should be aware of lower sensitivity (higher chance of false negatives) in EliA when interpreting anti-dsDNA test results.