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

ABSTRACT

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