ANA Prevalence in a Finnish Laboratory Cohort and the Impact of Confirmatory DFS70 Antibody Testing

Anti-DFS70 antibodies (DFS70Ab) are more commonly detected in healthy individuals than in patients with systemic autoimmune rheumatic diseases (SARD), making their recognition important in antinuclear antibody (ANA) testing. The nuclear dense fine speckled (AC-2) pattern associated with DFS70Ab can be difficult to identify using HEp-2 ANA indirect immunofluorescence (IIF), the standard ANA screening method, and AC-2–like patterns require confirmation with DFS70-specific assays. The prevalence of DFS70Ab in the Finnish population is currently unknown. We investigated DFS70Ab prevalence in a routine ANA cohort from Eastern Finland. In 2021, all routine ANA samples showing an AC-2 or AC-2–like IIF pattern were reflectively analyzed using the EliA™ DFS70 fluorescence enzyme immunoassay. Of 5,444 patients screened using the Kallestad HEp-2 ANA IIF assay, 84 (1.5%) exhibited an AC-2 or AC-2–like pattern, of whom 45.2% (38/84) were DFS70Ab-positive. Using our testing protocol, DFS70Ab prevalence was 0.9% in females and 0.4% in males (p = ns), accounting for 5.2% of all ANA-positive individuals. Notably, among females younger than 30 years, DFS70 accounted for 18.9% of ANA positivity. DFS70Ab prevalence was low in this Finnish ANA cohort compared with previously reported populations. Reflex DFS70 testing improved discrimination between true AC-2 patterns and AC-2–like patterns, supporting more accurate interpretation of ANA results in routine diagnostics.