Prevalence of Anti-Dense Fine Speckled 70 Antibodies in Systemic Autoimmune Rheumatic Diseases and Healthy Controls: A Cross-sectional Study

Introduction: Recognition of Dense Fine Speckled (DFS) Antinuclear Antibody (ANA) pattern is challenging as it is frequently confused with speckled or homogeneous patterns. Identification and confirmation of DFS pattern is important as it is more often seen in healthy individuals, routine laboratory referrals with relatively lesser prevalence in Systemic Autoimmune Rheumatic Diseases (SARD). As there is limited data on the prevalence of DFS pattern in Indian population, present study determined the prevalence and clinical significance of DFS pattern followed by anti-DFS 70 Enzyme Linked Immunosorbent Assay (ELISA) for confirmation. Aim: To estimate the prevalence of anti-DFS 70 antibodies in ANA screening tests, SARD, and healthy individuals by Indirect Immunofluorescence (IIF) screening and confirmation by anti-DFS 70 ELISA. Materials and Methods: A cross-sectional study was conducted over a period of 15 months from January 2017 to April 2018 at Department of Rheumatology, Nizams Institute of Medical Sciences, a Tertiary Care Institute in Hyderabad, Telangana, India. A total of 7,550 serum samples were tested by IIF during the study duration. Sera displaying DFS pattern was tested for anti-DFS antibodies and anti-Extractable Nuclear Antigen (ENA) antibodies by ELISA. A total of 49 patients from rheumatology department satisfying SARD criteria and 184 healthy patients were also tested for anti-DFS antibodies. Results: Anti-DFS 70 antibodies were seen in 0.47%, 16.3%, 39.6% among routine ANA screening referrals, SARD patients and healthy individuals, respectively. DFS 70 antibodies were positive in 60% of DFS IIF positive samples with none of them showing anti-ENA positivity or clinical evidence of SARD. Anti-DFS 70 positivity was more commonly seen in younger patients. Anti-DFS antibodies were significantly more common in healthy individuals compared to SARD patients (p-value=0.0022). Conclusion: It is important to confirm DFS IIF pattern with a specific ELISA as isolated DFS antibodies are frequently associated with non SARD conditions.