Use of ELISA to measure antinuclear antibodies in children with juvenile rheumatoid arthritis

Objective. To compare a series of commercial ELISA tests with an indirect i mmunofluorescent antibody (IFA) test for the detection of antinuclear antib odies (ANA) in children with juvenile rheumatoid arthritis (JRA). Methods, Sera from 178 patients with JRA (88 pauciarticular, 68 polyarticul ar, 22 systemic) were compared with 26 healthy pediatric subjects. Twenty-o ne samples from patients with systemic lupus erythematosus (SLE) were also tested. All samples were analyzed by IFA and by 3 commercial ELISA methods. Concordance of ELISA results with IFA results (selected standard) were use d as a measure of performance. Sensitivity and specificity were calculated for each test and likelihood ratios (LR) were established for IFA and ELISA in pauciarticular and polyarticular JRA sera. The increment in pretest pro bability was then obtained for each test as an additional measure of test p erformance. Results. IFA rendered positive results on 18-77% of the JRA sera depending upon the subset, 100% of SLE sera, and 15% of normal patient sera. Using IF A as the standard, correspondence with positive results among patients with JRA ranged from 0 to 74% for the 3 ELISA tests, while it ranged from 5 to 73% in IFA negative sera. IFA tests showed intermediate range likelihood ra tios (0.3, 0.5, 3.5, and 5) and increments in pretest probability ranging f rom 25 to 45%. While one of the ELISA tests attained 50% of increment in pr etest probability for the positive test, it showed 0% increment as a negati ve test. The other 2 ELISA tests incremented the pretest probability from 0 to 25%. Conclusion. Our findings indicate that in JRA, the lack of correspondence w ith the historic standard IFA precludes the use of ELISA tests for detectio n of ANA. In addition, IFA out-performs ELISA by a substantial degree when "clinical utility" analysis of test performance is utilized. Detection of A NA in children with JRA should either continue to rely on IFA or be based o n a different set of antigens if an ELISA format is chosen.