The clinical significance of borderline results of the Elia CTD Screen assay.

Background Data on the clinical relevance of borderline results of solid-phase assays in the screening for antinuclear antibodies (ANA) are sparse. This study aimed to determine the clinical significance of borderline results of the Elia CTD Screen (ECS; Phadia/Thermo Fisher Scientific, Freiburg, Germany), a fluoroenzymeimmunoassay incorporating 17 recombinant human nuclear antigens. Methods We retrospectively examined the medical records of 143 subjects with borderline ECS results for ANA-associated autoimmune disorders (AASARD) and the association with the results of indirect immunofluorescence (IIF) and confirmatory assays for ANA. Results AASARD were diagnosed in 10 patients (7%) with systemic lupus erythematosus (n=5; four patients were prediagnosed and in clinical remission), polymyositis overlap syndromes (n=2), scleroderma, Raynaud's syndrome and undetermined connective tissue disease (each n=1). Most frequently, homogeneous and nucleolar IIF patterns were found. Positive ANA subsets were observed in three patients. Furthermore, four patients were diagnosed with autoimmune liver diseases and yielded positive IIF in three and positive confirmatory assays in all cases. Taken together, 129 subjects had no AASARD. Within this group, 43 patients were IIF positive and most frequently showed speckled, unspecific nucleolar and only rarely homogeneous patterns. Positive ANA subsets were found in low concentrations near to the upper reference range in 18 subjects. Conclusions AASARD were observed in 7% of the subjects with borderline ECS and showed homogeneous or nucleolar IIF patterns in the majority of these cases. Our findings suggest that borderline results of the ECS can be clinically relevant and support the concept of a parallel or sequential screening for ANA by both ECS and IIF.