Background and objectives The dense fine speckled (DFS) anti-nuclear antibody (ANA) pattern, caused by anti-DFS70 antibodies, is often misunderstood due to its low association with systemic autoimmune rheumatic diseases (SARD) and presence in healthy individuals. Few studies suggest monospecific anti-DFS70 antibodies may exclude SARD. Given limited data from India, we aimed to assess the prevalence and clinical associations of anti-DFS70 antibodies in undefined disease, SARD, and controls. Methods Sera from patients with undefined disease and non-rheumatic disease controls were screened for DFS pattern during the evaluation for ANA by indirect immunofluorescence (IIF); positive samples were confirmed using anti-DFS70 ELISA and line immunoassay (LIA). SARD sera were tested by ANA IIF, ELISA, and LIA. Results DFS IIF pattern was observed in 0.25%, 0.57% and 0.4% of undefined disease referrals, SARD patients, and controls respectively. ELISA anti-DFS70 and LIA were positive in 90% of undefined disease sera, 15.4% vs. 5.7% of SARD cases, and 100% of controls, respectively. ELISA and LIA showed almost perfect agreement in undefined disease (κ= 0.861). In SARD group, anti-DFS70 ELISA positivity was predominantly observed in SLE (P=0.003); higher ELISA optical density, higher systemic lupus erythematosus disease activity index (SLEDAI) scores (P<0.001), anti-dsDNA (P=0.0001), and renal involvement (P=0.014) being significant observations. Monospecific anti-DFS70 antibodies by LIA were significantly common in undefined disease (P<0.001). Interpretation and conclusions DFS pattern with monospecific anti-DFS70 antibodies suggests lower likelihood of SARD. Anti-DFS70 antibodies are uncommon in SARD and coexist with other disease-specific autoantibodies. These findings highlight the complexity of interpreting anti-DFS70 antibodies and underscore the need for comprehensive serological testing and clinical correlation.
Keywords: Antinuclear; Autoimmune diseases; Immunoassay; India; Lupus erythematosus.