Clinical significance of anti-DFS70 antibody in antinuclear antibody-positive samples with a dense fine speckled pattern

Background: When the dense fine speckled (DFS) patternantinuclear antibodies (ANA) are detected in the indirect immunofluorescence (IIF) assay, the presence of antidense fine speckles 70 (DFS70) antibodies has been suggested to facilitate the exclusion of ANA-associated rheumatic diseases (AARD). We evaluated the potential use of anti-DFS70 antibodies for verifying AARD in patients with a positive ANA result of the DFS pattern. Methods: A total of 5509 patients who were requested ANA testing were included. The DFS pattern was confirmed using two IIF assays. Semiquantitative DFS70 ELISA (Euroimmun, Germany) was examined in samples with the DFS pattern. Results: Among 639 ANA-positive patients, 19.6% displayed the DFS pattern. And 17.6% of patients with the DFS pattern were diagnosed with AARD. The low titer of 1: 80 was more prevalent in the non-AARD group than in the AARD group (64.1% vs. 4.5%, p < 0.0001). Anti-DFS70 antibodies were positive in 60.0% of patients with the DFS pattern. The frequency of anti-DFS70 positivity was higher in the non-rheumatic disease (NRD) group (74.2%) than in the other rheumatic disease group (43.2%, p = 0.003) and the AARD group (45.5%, p = 0.019). Conclusions: The DFS pattern is present in both AARD and non-AARD cases. In the DFS pattern, a low titer of 1: 80 and isolated anti-DFS70 antibodies without AARDassociated antibodies represent a low likelihood of AARD. The presence of anti-DFS70 antibodies cannot exclude AARD and should be analyzed in combination with AARD-associated antibodies in the diagnostic algorithm.