The dense fine speckled (DFS) nuclear pattern is one of the most common indirect immunofluorescence (IIF) patterns detected during routine anti-nuclear antibody (ANA) screening. There is a negative association between anti-DFS70 status and systemic autoimmune
rheumatic disease (SARD), especially in the absence of concomitant SARD-specific
autoantibodies. The purpose of this study was to determine the need for confirming anti-DFS70 status when a DFS pattern is observed in IIF-ANA. The frequency of anti-DFS70 detection on Western blot and the positive rate of
connective tissue disease (CTD)-related
autoantibody screening with a fluorescence-based
enzyme immunoassay was evaluated in DFS (n = 182) and non-DFS (n = 359) groups. Specific
autoantibodies against 15
autoantigens were identified by line immunoassay. We evaluated the frequency of cases of DFS mistaken for non-DFS and non-DFS cases mistaken for DFS, as well as the clinical impacts of these misinterpretations. Among cases of IIF-ANA with an observable DFS pattern, 68.1% had only anti-DFS70 without CTD-related
autoantibodies, 20.3% were false positive for IIF-ANA, and the remaining 11.5% had CTD-related
autoantibodies independent of anti-DFS70 status. These results indicated that CTD-related
autoantibodies may be present with or without anti-DFS70 even if a DFS pattern is observed in IIF-ANA. Among patients who are ANA negative or have a low probability of SARD, an anti-DFS70 confirmation test has no clinical benefit and cannot replace specific tests for detecting CTD-related
autoantibodies. Specific tests to detect CTD-related
autoantibodies should be performed instead of anti-DFS70 confirmation tests when a DFS pattern is observed in IIF-ANA.