Antinuclear antibodies (ANA) screening by enzyme immunoassay with nuclear HEp-2 cell extract and recombinant antigens: analytical and clinical evaluation

Abstract

Objectives Immunofluorescence assay (IFA) has been the standard method for antinuclear antibodies (ANA). To simplify and standardize the ANA test, generic ANA solid phase enzyme immunoassay has been promoted. The objective of the present work has been to study the relationship with IFA and the clinical usefulness of a generic EIA for ANA (COBAS Core HEp-2 ANA EIA, Roche Diagnostics). Design and methods We studied 74 healthy individuals, 119 patients with defined systemic autoimmune diseases, 26 patients with other autoimmune diseases, and 490 routine samples sent to laboratory for ANA analysis. Results Precision study showed intra-assay coefficient of variations (CVs) below 8% and inter-assay CVs below 10%. In relation to IFA, a 0.6 kappa index of agreement was obtained. COBAS-ANA concentrations increased according to IFA titer and greatest COBAS-ANA responses were obtained with pure or mixed homogeneous patterns and centromeric patterns. Analysis of COBAS-ANA response to particular antigenic specificities showed that SS-B, Scl-70 and U1sn-RNP specificities were saturating at high concentrations, whereas Jo-1, SS-A and nuclear and centromeric specificities exhibited lower responses. Elevated serum concentrations of IgG and IgM did not interfere COBAS-ANA, but high serum rheumatoid factor (RF) concentrations produced a decrease of ANA. For systemic lupus erythematosus (SLE) patients, the COBAS-ANA best efficiency was obtained with a cut-off of 0.9, with a sensitivity of 97% and a specificity of 88%, whereas the best IFA-ANA efficiency was obtained with a 1:80 dilution, giving a sensitivity of 90% and a specificity of 99%. There were no differences between areas under ROC curves for COBAS-ANA and IFA-ANA. For other systemic and nonsystemic autoimmune diseases sensitivity and specificity of COBAS-ANA were similar or higher than that of 1:160 IFA-ANA titer. Conclusion Sensitivity and specificity of COBAS Core ANA-EIA for SLE and other systemic and nonsystemic autoimmune diseases, together with performance characteristics make it an adequate automated system for ANA screening.