Evaluation of anti-ds DNA antibody measurement by using commercial kits for use in a clinical laboratory

Three hundred and seventy-six consecutive antinuclear antibody-positive sera were tested for anti-ds DNA antibody by using three commercial kits which use 125 I recombinant DNA (radioimmunoassay), highly purified calf thymus DNA (enzyme linked immunosorbent assay) and Crithidia lucilliae (immunofluorescence assay) as substrates. All patients' sera, after reviewing medical records, were classified into three broad groups: Group I (systemic lupus erythematosus), Group II (rheumatic diseases and rheumatoid arthritis), and Group III (nonspecific ANA antibody test positive). A sensitivity, specificity, positive predictive test value and negative predictive test value for Group I against Group II-III (generally these two groups of sera should not show any anti-ds DNA antibody) combined showed for Crithidia lucilliae (IF assay) 58.8%, 93.6%, 82% and 82%, for 125 I recombinant DNA (RIA) assay, 75.8%, 94%, 86.2% and 88.7% and calf thymus highly purified DNA (ELISA) assay using positive cut-off value >100 U/mL, 97.5%, 35%, 42.9% and 24%. The 125 I recombinant DNA (RIA) assay based on the principle of the Farr technique, which is still considered to be the gold standard for anti-ds DNA antibody detection, showed the best specificity and sensitivity among all three methods tested in this study.