The presence of anti-dsDNA is included in diagnostic criteria for systemic lupus erythematosus (SLE) according to the American College of Rheumatology (ACR). It has been the most useful factor in the diagnosis, prognosis, and therapeutic monitoring of patients with SLE. A number of methods are available but radioimmunoassay (RIA) has been regarded as standard method. A shift from RIAs to nonisotopic assay has been observed with other tests. Still, RIA assays are standard methods for anti-nDNA antibodies. A comparative study of the Crithidia luciliae immunofluorescence (CLIF) assay and an RIA was made. METHOD: Sera from 144 patients were tested by an indirect immunofluorescent antibody technique employing Crithidia luciliae and IT-1 cell lines as a substrate and radioimmunoassay was based on the Farr technique. RESULTS: 1. Thirty-nine of 122 sera with positive antinuclear antibody (ANA) tests had the possibility of positive anti-nDNA antibodies. 2. The RIA was positive in 54 sera, and 37 of these showed a discrepancy between the RIA and the ANA pattern (false positive rate 25.7%). 3. The CLIF was positive in 15 sera, and 5 of these showed a discrepancy between CLIF and the ANA pattern (false positive rate 3.5%). 4. Only CLIF was positive in 2 sera of which one showed a discrepancy between CLIF and the ANA pattern. 5. Only RIA was positive in 41 sera, and 33 of these showed a discrepancy between RIA amp; the ANA pattern. CONCLUSION: The immunofluorescence assay using Crithidia luciliae is a valid method to detect anti-dsDNA antibodies and has a much lower false positive rate compared with RIA. The simple and inexpensive CLIF test could either replace the RIA in clinical laboratories or be used in conjunction with the ANA pattern as a confirmatory test for antibodies to nDNA.
Antibodies* ; Antibodies, Antinuclear ; Cell Line* ; Crithidia* ; Diagnosis ; Fluorescent Antibody Technique ; Humans ; Lupus Erythematosus, Systemic ; Prognosis ; Radioimmunoassay ; Rheumatology