Screening of antinuclear antibodies: comparison between enzyme immunoassay based on nuclear homogenates, purified or recombinant antigens and immunofluorescence assay

Current clinical practice considers antinuclear antibody (ANA) testing as a screening test; this has a major impact on laboratory work with a growing volume of analyses that need to be performed rapidly, to maintain good specificity and sensitivity. Ongoing discussions have been raised in order to identify the best technology to use in ANA screening, taking into account both clinical and economical implications. The aim of our study was to compare three different enzyme immunoassays (EIA) with immunofluorescence (IF) assay in order to identify which test is better for use as a screening test. The study was performed on 473 sera and the three different EIA tests were based on nuclear homogenates from HeLa cells, purified antigens from HEp-2 cells and recombinant antigens, respectively. The concordance between EIAANA and IFANA techniques, determined by the kappa statistic, was acceptable, but not complete, and discrepancies between both EIApositive/IFnegative samples and IFpositive/EIAnegative were found. Both methods show interesting diagnostic abilities, however, the IFANA assay seems to be the first choice test in a wellstandardized immunofluorescence laboratory with experienced microscopists, whereas the EIA test might be useful especially in largescale ANA screening.