Among anti-double-strand (ds)DNA antibody assays, Farr radioimmunoassay is decreasingly used because it requires radioactive material and is labor intensive. We evaluated the performance of Farr, three commercial enzyme immunoassays (EIAs) and the Crithidia luciliae immunofluorescence test (CLIFT) in systemic lupus erythematosus (SLE).
Anti-dsDNA antibodies were determined in 99 SLE patients, 101 healthy subjects, and 53 patients with autoimmune rheumatic diseases.
Farr performed better than the 3 EIAs and CLIFT for the diagnosis of SLE at the manufacturer's cut off and at the cut off set to achieve a specificity of 95%. To achieve a similar level of specificity, some EIAs had a decrease in sensitivity which was dramatic for some tests. Farr was also the best at distinguishing patients with quiescent to mildly active disease from patients with more active disease at the cut off value of 93 IU/ml. Using manufacturer's cut off did not allow distinguishing between patients with quiescent and active SLE.
Farr was the best global test to assess the level of anti-dsDNA antibodies for both diagnosis and disease activity evaluation in SLE with adequately determined cut off values. Some EIA had low performances limiting their use in decision-making regarding diagnosis and/or treatment.