Purpose Patients with Systemic Lupus Erythematosus (SLE) and Sjogren’s Syndrome (SS) sometimes share common clinical features and can have similar autoantibody profiles. We evaluated a group of patients with each disease to determine which features distinguish each group.

Methods Samples (n=1000) were identified based on the clinical ANA results obtained by EIA (BioRad). This testing was performed on the Triturus semi-automated platform (Grifols) in accordance with all the manufacturer’s instructions. Samples were selected for this study to be distributed across the reportable range of the ANA EIA method (n=273 negative [<1.0 U], 225 weak positive [1.1–2.9], 250 positive [3.0–5.9], 252 strong positive [>5.9]. All samples selected for this study were subsequently analysed by multiplex assay (MIA) for specific autoantibodies. The MIA testing was performed on the BioPlex 2200 (BioRad). All samples were from adults age >18 years).

Results Out of 1000 samples there were 227 patients with connective tissue disease including 67 with SLE and 42 with SS. We compared the SLE patients with those who had SS.

The SLE patients were younger than those with SS. (Mean age 47.4 years, median 47, range 19–81 vs Mean age 56.5 years, median 59, range 19–76, P 0.001). There was no difference in sex distribution (82% female vs 86% female).

Conclusions Somewhat surprisingly, the presence of anti-DsDna and anti-Smith antibodies was not the best way to separate the patients. The best combination of variables to distinguish SLE patients from those with SS was younger age, the presence of anti-chromatin antibodies and the absence of anti-SSA antibodies.