Immunofluorscense - still the 'gold standard' in ANA testing?

Abstract

A usefulness of enzyme immunoassay (EIA)-based antinuclear antibodies (ANA) tests was evaluated in comparison with the immunofluorescence ANA assay (IF-ANA). COBAS-ANA and MBL-ANA were used, in the former a mixture of antigens extracted from HEp-2 cells and multiple recombinant antigens was immobilized on beads as the antigen, and in the latter 9 kinds of purified or recombinant proteins are immobilized on 96-well plates. We first compared an ability to differentiate 258 connective tissue disease (CTD) patients (except rheumatoid arthritis) from 257 healthy subjects between COBAS-ANA and IF-ANA. The sensitivity and specificity of COBAS-ANA were 84 % and 94 %, respectively, while those of IF-ANA at a cutoff dilution of 1:160 were 81 % and 87 %. The receiver operating characteristic (ROC) analysis showed a significant superiority of COBAS-ANA to IF-ANA. Moreover, when the cutoff index was set at 0.6, the COBAS-ANA could detect the 8 disease-specific ANAs as well as IF-ANA at a cutoff dilution of 1:40. A possible availability of MBL-ANA in a periodic health examination in certain towns was also demonstrated. Among the 1123 subjects, a total of 145 disease-specific ANAs were detected in 126 subjects. MBL-ANA could catch disease-specific ANAs with almost same efficacy of IFANA. Annual survey of the residents by MBL-ANA may lead to a detection of CTD patients. EIA-based ANA tests are very useful for both detecting disease-specific ANAs and screening CTD patients. We believe that EIA-ANA should be the 'gold standard especially for screening a large number of samples, although there is some room for technical improvement.