Predictive value of antinative dna for systemic lupus erythematosus: Comparison of radioimmunoassay and enzyme immunoassay

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Abstract
Positive predictive values for the diagnosis of systemic lupus erythematosus (SLE) were determined for two antinative DNA assays: a Farr‐type radioimmunoassay (RIA) and a solid‐phase enzyme immunoassay (EIA). The study population consisted of all patients whose EIA anti‐DNA results were positive (>250 IU) during a 150 day period; in addition all patients whose EIA anti‐DNA results were 100–50 IU during the first 25 days of this period were also included. Simultaneous Farr RIA were performed on all sera, and the Crithidia luciliae immunofluorescent assay was also carried out on those with positive RIA and/or EIA results. Diagnoses were established by chart review, and disease activity was scored for SLE patients. Positive predictive values for SLE were dependent on the level of test positivity, and “normal” limits of 10% binding for the Farr RIA and 800 IU for the EIA gave comparable results. Combination with Crithidia luciliae immunofluorescence increased the sensitivity of both assays, especially the EIA. Results of both assays correlated significantly with activity scores in SLE patients.