All samples were also tested for the presence of anti-dsDNA antibodies by chemiluminescence immunoassay (QUANTA Flash, Inova Diagnostics) as previously described (27 (link)) using a cutoff of 70 IU/ml, established in accord with the SLICC classification criterion for anti-dsDNA positivity, which requires that the cutoff for the anti-dsDNA antibody level be above the laboratory reference range (or >2-fold the reference range if tested by enzyme-linked immunosorbent assay) (5 (link)).
Antibodies to proliferating cell nuclear antigen, ribosomal P, recombinant Ro 52/TRIM21, native SSA/Ro 60, SSB/La, Sm, and U1 RNP were detected using the extractable nuclear antigen FIDIS Connective Profile, kit 13 addressable laser bead immunoassay (TheraDiag) on a Luminex 200 flow luminometer, according to the manufacturer’s instructions, and using MLX-Booster software. Other autoantibodies, such as IgG anticardiolipin, IgG anti–β2-glycoprotein 1, and lupus anticoagulant, were measured in a central laboratory as previously described (28 (link)). ANA IIF patterns were classified according to the new ICAP standards (http://www.anapatterns.org/index.php) (9 (link)).