Detection of antibodies to extractable nuclear antigens (ENAs) is needed for the diagnosis in systemic autoimmune diseases. In this study, we compared three reagents using line immunoblot assay (LIA) or multiplex bead immunoassay for detecting the anti-ENAs.

A total of 89 sera were tested by 3 different assays: EUROASSAY Anti-ENA Profile (Euroimmune, Germany), Polycheck Autoimmune Test (Biocheck GmbH, Germany), and FIDIS™ Connective Profile (Biomedical Diagnostics, France). The following individual ENAs were investigated: Sm, SS-A (Ro), SS-B (La), Scl-70, Jo-1 and RNP. We reviewed medical records to investigate the discrepant results among three methods.

Overall percent agreements were 96.1% between EUROASSAY Anti-ENA Profile and FIDIS™ Connective profile; 90.4% between EUROASSAY Anti-ENA Profile and Polycheck Autoimmune Test using the manufacturers’ cutoff; 96.4% between EUROASSAY Anti-ENA Profile and Polycheck Autoimmune Test using a upward cutoff; 90.4% between FIDIS™ Connective profile and Polycheck Autoimmune Test the manufacturers’ cutoff; and 96.4% between FIDIS™ Connective profile and Polycheck Autoimmune Test a upward cutoff.

The three assays showed excellent agreement with each other. With appropriate cutoff, the all three assays for six of the anti-ENA tests investigated in this study can be used in clinical laboratories for detecting the anti-ENAs.

The purpose of this study is to compare newly developed assay for identification of ENA antibody, Phadia EliA ENA with Euroimmun line immunoassay by analyzing the degree of agreement and the individual antibodies between two methods.

A total of 82 patient samples were used. Indirect immunofluorescence assay using Hep-2 cell was performed to screen the antinuclear antibody (ANA). Euroimmun line immunoassay (LIA) and Phadia EliA ENA assay were tested to identify the antibodies against extractable nuclear antigens (ENAs). Kappa statistics was used to evaluate the degree of agreement.

Mean age of patients was 41.0 (8-79), and the M:F ratio was 21:61. ANA was positive in 74 samples, and negative were 8 samples. Kappa analysis of the 82 tested samples showed a moderate strength of agreement (κ = 0.521, P = 0.000). There were differences in the order of identified individual antibodies between two methods (Ro > La = RNP > Centromere > Sm > Scl-70 in Phadia EliA ENA, Ro > RNP > Sm>La > Scl-70 > Centromere=Jo-1 in Euroimmun LIA). Ro antibody was most frequently identified in Phadia EliA ENA negative-Euroimmun LIA positive specimens (Ro > RNP = Jo-1 > La = Sm = Centromere > Scl-70).

A moderate strength of agreement was observed between the Phadia EliA ENA and the Euroimmun LIA. There seemed to be a significant difference in the ratio of individual antibodies, especially in the anti-Ro and Sm antibodies.