Detection of dsDNA antibodies using the Phadia EliA immunoassay

Antibodies to double-stranded DNA (dsDNA) are present in up to 90% of patients with systemic lupus erythematosus (SLE) and may show correlation with disease activity. Laboratory testing for SLE at ACT Pathology involves first screening with the highly sensitive Bioflash chemiluminescence assay. Confirmatory testing of positive samples is performed using the more specific Crithidia luciliae immunofluorescence test (CLIFT). Discordant results are further evaluated using the Farr radioimmunoassay (Farr-RIA), the highly specific and widely accepted gold standard. We performed an audit using 46 samples, including both patient and RCPA quality assurance samples, to evaluate the concordance of the Phadia EliA immunoassay with our existing methods. In patients who do not have SLE, the Phadia Elia showed a high level of concordance with all confirmatory existing assays (CLIFT 84.6%; Farr-RIA 92.3%), demonstrating a high negative predictive value. Among the patients with SLE, the overall concordance was 68.4% with Bioflash and 66.7% with CLIFT, showing higher inter-assay differences in this population. Taken together, the Phadia Elia appears to be an effective immunoassay to exclude SLE and may represent an alternative to the Farr-RIA when clinical turnaround time is critical.