It is has been proposed that the presence of anti-DFS70 antibodies could be used to eliminate a SARD diagnosis. However, anti-DFS70 antibodies were also observed at relatively high frequency in patients with SARD. The clinical significance of these antibodies is therefore not yet clear. In this study, we assessed the clinical significance of the presence of anti-DFS70 antibodies.
A total of 3432 sera samples were obtained from patients who underwent routinely requested ANA screening in the clinical laboratory of a University Hospital, between June 2017 and June 2019. Antinuclear antibody testing was performed by indirect immunofluorescence (IIF) on Hep-2 cell substrates (Euroimmun, Germany), and anti-ENA were measured by LIA (Euroimmun, Germany).
Among 3432 serum samples tested for ANA, 57.3% were ANA positive by IIF. Participants had mean age of 46.4 and 74.8% of the participants were female. Only 11.4% of the study population had SARD. The frequency of DFS pattern by IIF was 8.1%. Analysis of the DFS pattern positive samples by LIA revealed the presence of anti-DFS70 autoantibodies in 67.5% of all DFS, AC-2 pattern ANAs. When using the results of the ANA IIF HEp-2 DFS pattern/Anti-DFS70 LIA, likelihood ratio (LR) for SARD was 0.33. When comparing the ANA IIF HEp-2 DFS pattern with anti-DFS70 LIA, the ANA IIF HEp-2 DFS pattern's LR was lower (0.63 vs 0.85).
Although the DFS pattern cannot exclude the presence of SARD, the likelihood is lower than with other patterns. Therefore, anti-DFS70 antibodies represent an important biomarker that can aid in the interpretation of positive ANA patients and, therefore, should be included in test algorithms for ANA testing. The optimal test algorithm might be laboratory specific being dependent on referral patterns for ANA testing.