Specific chemoluminescence and immunoasdorption tests for anti-DFS70 antibodies avoid false positive results by indirect immunofluorescence

Objective: To evaluate two new diagnostic methods for the identification of anti-DFS70 antibodies in samples showing a DFS70-staining pattern by indirect immunofluorescence (IIF).

Methods: We studied 731 patients: 576 were collected consecutively among those that in the ANA test on HEp-2 cells had produced a DFS70 fluorescence pattern and 155 were a consecutive series of patients sent by referring physicians for routine ANA testing. As controls we studied 50 patients with autoimmune diseases and 120 patients with active infectious disease. All 731 sera were assayed for anti-DFS70 antibodies by a specific chemoluminescence assay (CLIA); 70 randomly selected IIF-positive sera and 35 samples from patients with autoimmune diseases were studied by inhibition tests using the HEp-2 Select method.

Results: Assays performed with the CLIA-DFS70 method were positive in 30.4% of the samples presenting a DFS70 pattern by IIF, in 1.3% of the routine ANA sera, in 1.6% of the infectious sera and in none of the 50 autoimmune controls. However, as the IIF-DFS70 positive group included 106 patients with systemic autoimmune rheumatic diseases (SARD), 11 of which were DFS70 positive by CLIA, the prevalence of DFS70 antibodies in SARD was 7.5%. The ANA test performed after the use of HEp-2 Select showed an inhibition in 95.7% of the sera. No change in fluorescence intensity and pattern morphology between the native sera and the same sera tested with the solution containing the DFS70 antigen was observed in the 35 samples from patients with autoimmune diseases.

Conclusions: To avoid misinterpretation of ANA pattern and consequent diagnostic errors, confirmation of the DFS70-IIF pattern by CLIA or other specific methods is mandatory before reporting the presence of anti-DFS70 antibodies. The HEp-2 Select test in most cases eliminates the interference by anti-DFS70 antibodies and avoids the possible reporting of false positive results.