Background Autoantibodies to extractable nuclear antigens (ENAs) are important diagnostic markers for autoimmune diseases but have some limitations, since no gold standard has been established. We compared two current assays commonly used.
Objectives An automated fluorescent enzyme immunoassay (FEIA), Phadia® 250 (Phadia, Sweden), is being compared with microplate ELISA assay (INOVA Diagnostics, USA) for the detection of five commonly used anti-extractable nuclear antigens.
Methods A total of 100 serum samples from the patients with systemic rheumatic diseases were collected and assayed with the Phadia® 250 (Phadia, Sweden) and microplate ELISA (INOVA Diagnostics, USA) for 5 anti-extractable nuclear antigens.
Five kinds of autoantibodies to SSA/Ro, SSB/La, RNP, Sm, and Scl-70 were performed using respective QUANTA Lite™ ELISA kits (INOVA Diagnostics, USA) and Phadia® 250 assays.
The statistical analysis of agreement rate with kappa coefficient, sensitivity and specificity of each assays were performed with Analyse-it® for Microsoft Excel 3.90.4 (Analyse-it Software, Ltd.)
Results The concordance rates between ELISA and Phadia® 250 ranged from 89% for anti-RNP to 97% for anti-Scl-70, and the kappa coefficients between the results by the two assays were from 0.44 to 0.82 (Table1). There were no significant differences in sensitivities and specificities of each anti-ENA between the two assays except for specificity of anti-RNP and sensitivity of anti-Sm. The overall sensitivities of antibodies to SS-A/Ro (0.760-0.840), SS-B/La (0.200-0.120) and RNP (0.560-0.400) in SLE group were quite similar for the two methods. Specificities of antibodies to SS-A/Ro (0.338-0.351), SS-B/La (0.689-0.730), RNP (0.824-0.919) and Sm (0.959-0.986) in SLE group also indicated similarity between the two assays. There were no significant differences in sensitivities and specificities of each antigen in Sjögren group except for sensitivity of anti-RNP.
Conclusions FEIA method by automated Phadia® 250 showed comparable results with those by conventional ELISA for detecting anti-ENAs. Automated FEIA by Phadia® 250 could be a useful method in that it provides shorter protocol time, simpler use of methodology.
Disclosure of Interest None declared