Evaluation of an ELISA method for the measurement of antibodies to dsDNA.

Anti-dsDNA is found in 60-70% of patients with active, untreated systemic lupus erythematosus (SLE) and its detection serves as an important tool in the diagnosis and monitoring of these patients. This study evaluates the use of an Enzyme Linked Immunosorbent Assay (Elisa) to detect these antibodies. Its performance is also compared to the older, but established, method of detecting anti-dsDNA using Crithidia luciliae. The sera of the 56 normal healthy blood donors revealed a mean anti-dsDNA titre of 0.93mg% with a standard deviation of 0.23mg%. All 14 patients found to be negative by the Elisa method and 10 of the 11 patients found to have borderline anti-dsDNA Elisa titres were negative by immunofluorescence. 35 patients were found to harbour raised titres of anti-dsDNA by the Elisa method. All patients found to have anti-dsDNA titres exceeding 2mg% by the Elisa test were also positive by immunofluorescence. In fact, those with very high titres by the Elisa test were also strongly (titre greater than 1:100) positive by immunofluorescence. As a measurement of the kit's accuracy, the percentage of recovery of the activity of known amounts of antibody in a specimen fell within the range of about 89-104%. As a measurement of the kit's reproducibility, the coefficient of variation in the assayed titres of sample replicates was found to be 7.5% for within-batch assays and 9.7% for between-batch assays. The Elisa assay compared favourably to the immunofluorescence test in terms of enhanced sensitivity, quantitative approach with an objective end-point and the large number of samples that may be assayed simultaneously.