The performance of immunoassays for the detection of autoantibodies is of critical importance to the diagnosis and assessment of patients with systemic lupus erythematosus (SLE). Our objective was to compare 3 multiplexed assays for measurement of multiple autoantibodies and their association with global disease activity, active nephritis and cumulative organ damage in systemic lupus erythematosus (SLE). Stored sera, clinical and laboratory data from the enrollment visit of a long-term lupus registry were used. Autoantibodies were measured using the BioPlex 2200 ANA screen (Bio-Rad), QuantaPlex ENA8 (INOVA Diagnostics) and recomLine ANA/ENA (Mikrogen). The analytes included dsDNA, chromatin, ribosomal P protein, SS-A/Ro60, Ro52, SS-B/La, Sm, U1-RNP, centromere B, topoisomerase 1 and Jo-1 (histidyl tRNA synthetase). Global SLE disease activity was measured by the SLE disease activity index (SLEDAI) and cumulative organ damage by the SLICC/ACR damage index (SDI). One hundred ninety two patients (87% female; 91% Caucasian; mean disease duration 8.8years) were studied. Agreement between the 3 assays varied from 70% to 99% (Cohen's kappa: 0.04-0.88). There were significant associations between SLEDAI scores (excluding anti-dsDNA) and ANA (INOVA, Mikrogen), anti-dsDNA (Bio-Rad, Mikrogen), anti-chromatin (Bio-Rad, INOVA), anti-Ro (Mikrogen), anti-Sm and anti-U1-RNP (all 3 immunoassays) (p=0.002-0.05). Concurrent lupus nephritis was associated with anti-dsDNA (Bio-Rad (p=0.017) or Bio-Rad and Mikrogen together (p=0.015)). There was no significant association between autoantibodies and SDI scores. The overall agreement between assays for the detection of autoantibodies was reasonable. The greatest discordance (70-83%) occurred with those autoantibodies most strongly associated with global SLE disease activity (ANA, anti-dsDNA, anti-chromatin and anti-Sm). Furthermore, there were differences between assays in their associations with global SLE disease activity and lupus nephritis.
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