Comparison of the clinical utility of the Elia CTD Screen to indirect immunofluorescence on Hep-2 cells.

Background: We compared the Elia CTD Screen (ECS), a fluoroenzymeimmunoassay incorporating 17 human antinuclear antigens (ANA), with indirect immunofluorescence (IIF) on Hep-2 cells in order to determine the clinical utility of the ECS in additon to or without IIF.

Methods: We examined 1708 consecutive serum samples submitted for ANA testing using the ECS and IIF in parallel. Positive screen results were further examined by quantitative fluoroenzymeimmunoassays and/or immunoblots for antibody identification. The medical records were evaluated for systemic rheumatic disorders.

Results: Concordance between ECS and IIF was observed in 1344 (78.8%) samples. ECS had a better detection rate for anti-dsDNA, -SSA/Ro, -SSB/La, -U1RNP and -Jo-1 antibodies, whereas IIF was superior in the detection of anti-CENP-B antibodies as well as anti-histone, -nucleosome and -Pl-12 antibodies, which are not included in the ECS antigen panel. ECS had a 100% sensitivity for Sjögren's syndrome, systemic sclerosis and Sharp syndrome. The sensitivity for Sjögren's syndrome was slightly higher for ESC than for IIF (94%). IIF had a higher diagnostic sensitivity for systemic lupus erythematosus, indeterminated connective tissue disease, Raynaud's syndrome and limited scleroderma, compared to ESC (100% vs. 80%, 100 vs. 75%, 89 vs. 57%, 100 vs. 88.9%).

Conclusions: Our results suggest that the ECS represents an appropriate diagnostic tool for ANA screening. However, since some antigens are not incorporated in the ECS panel, and some ANA can also be missed by IIF, sequential or parallel screening with ECS and IIF may be reasonable when the clinical suspicion for connective tissue disease is high.