AB1044 Evaluation of a fluoroenzyme immunoassay (ELIA-CTD) in the screening of patients suspected for autoimmune connective tissue diseases
Authors: M Elkhalifa, R Abdulhadi, H Ramadan, S Barrientos, S Saleh, O Alsaed, A-W Al-Allaf
Journal: Annals of the Rheumatic Diseases (2017)

<h3>Background</h3> Detection of auto-antibodies directed against nuclear antigens (antinuclear antibodies or ANA) have important diagnostic and prognostic implications in connective tissue diseases (CTD). The conventional indirect immunofluorescence assay on HEp-2 cell line (ANA-IIF) is the most commonly used method to detect ANA. The ANA-IIF can be labor intensive and suffers from lack of specificity. <h3>Objectives</h3> To evaluate the utility of a new fluoroenzyme Immunoassay "EliA-CTD" as an alternative for screening patients suspected for autoimmune connective tissue diseases. <h3>Methods</h3> Sixteen Hundread (1600) consecutive patients9 sera submitted for anti-nuclear antibodies were tested using the ANA-IIF (Diasorin S.P.A, Saluggia, Italy) and the new EliA-CTD screen (Phadia GmbH, Frieiburg, Germany). ANA testing was ordered by both primary and secondary care physicians. The EliA-CTD screening assay is a fluoroenzyme immunoassay which is performed on the Phadia-250 automated platform. The EliA–CTD assay contains ANA-targeted recombinant antigens including dsDNA, Sm-D, Rib-P, PCNA, U1-RNP (70, A, C), SS-A/Ro, SS-B/La, Centromere B, Scl-70, Fibrillarin, RNA Polymerase III, Jo-1, Mi-2, and PM-scl. The test results are expressed as ratio, with &gt;1.0 considered positive. For ANA-IIF, the cut off for positive results was 1:40 or greater. Additionally, further testing for dsDNA and other extractable nuclear antigens (ENA) was undertaken on a subset of sera that were ANA-IIF+ or whenever there was discrepancy between the two methods. <h3>Results</h3> The overall agreement between the two methods was 84.2%. Three hundread and eight (308) out of 1600 (19.3%) samples tested positive by ANA-IIF positive as compared to 101/1600 (6.6%) for the EliA-CTD assay. Additional testing showed that 105 samples were positive for ENA including dsDNA. Of those, 101 were EliA-CTD positive and 81 were ANA-IIF positive. By incorporating the ENA results, the calculated sensitivity and specificity for the EliA-CTD were 97.1% and 99.7% respectively with positive and negative predictive values for the EliA-CTD assay of 96.1% and 99.8%, respectively. The corresponding sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the ANA-IIF assay at different dilutions is shown below: <h3>Conclusions</h3> The new automated EliA-CTD assay shows superior sensitivity and specificity compared to the conventional labor intensive ANA-IIF. The EliA-CTD can be used as an upfront screening tool for connective tissue diseases. Depending on the clinical details, any EliA-CTD positive results could be reflexly followed by additional testing including ANA-IIF testing to elucidate the titer and pattern. <h3>References</h3> Hayashi N, Kawamoto T, Mukai M, Morinobu A, Koshiba M, Kondo S, Maekawa S, Kumagai S. Detection of Antinuclear Antibodies by Use of an Enzyme Immunoassay with Nuclear HEp-2 Cell Extract and Recombinant Antigens: Comparison with Immunofluorescence Assay in 307 Patients. Clinical Chemistry 2001; 47(9):1649–1959. <h3>Disclosure of Interest</h3> None declared