Background ANA are a diagnostic hallmark of SLE and others systemic autoimmune rheumatic diseases (SARD). Different methods have recently been developed for automated ANA detection, including IIF-HEp-2 interpretation systems, ELISA and multiplex immunoassay.
Objectives The aim of the study was to compare the diagnostic performance of three automated methods for ANA detection (IIF-HEp-2, ELISA and BioPlex 2200) in SLE patients (pts).
Methods We studied 94 pts (80 F, age 35.9[16.0;65.0] years, disease duration 113.5[2.0-576.0] months) with SLE (ACR criteria, 1997), 50 pts with others SARD, 20 pts with non-autoimmune RD and 30 healthy controls (HC). Serum samples were evaluated for the presence of ANA using automated IIF-HEp-2 system AKLIDES (“Medipan GmbH”, Germany), ELISA analyzer ALEGRIA (“Orgentec”, Germany) and automated multiplexed immunoassay system BioPlex 2200 ANA Screen (Laboratories Inc. Hercules, CA, USA). Positive results of ANA detection were corresponding to the following values: ≥1:160 (IIF-HEp-2), ≥1.3 U (ANA Screen, ELISA), ≥25.0 U (antigen-specific ANA, ELISA), ≥1.0 AI (antibody index) (BioPlex). Positive cutoff values for anti-dsDNA were ≥20.0 IU/ml (ELISA) and ≥10.0 IU/ml (BioPlex).
Results The kappa agreement coefficients between IIF and ELISA, IIF and BioPlex were lower compared to ELISA and BioPlex (0.438,0.426, vs 0.726) for ANA screening. In SLE pts, ANA detection by IIF showed a higher diagnostic sensitivity than ELISA and BioPlex (0.97 vs 0.80, 0.83). The rate of false negative results was 3% for IIF, 20% for ELISA, 17% for BioPlex. The overall specificity (Sp) of the ANA screening test with IIF was lower than the Sp of ELISA and BioPlex (0.40 vs 0.70, 0.57). In HC group, the Sp of ANA detection was similar between IIF (0.93) and ELISA (0.97), while BioPlex ANA Screen had the lowest Sp (0.80). Negative test results by IIF had a lower likelihood ratio (LR) than ELISA and BioPlex (0.08 vs 0.29, 0.30), indicating that IIF was better to exclude SLE diagnosis. The agreement between ELISA/BioPlex testing for antibodies to dsDNA, Sm, RNP-70, Ro/SS-A (52/60 kD), La/SS-B was good (kappa=0.567, 0.673, 0.775, 0.816, 0.777, respectively). Both methods had a high diagnostic Sp for the detection of anti-dsDNA (0.94/0.95), anti-Sm (0.97/0.97) and anti-RNP (0.94/0.95) in SLE. Positive LR of anti-dsDNA and anti-Sm antibodies testing by ELISA/BioPlex (11.50/10.42 and 7.10/9.57) demonstrated the most useful values for SLE diagnosis.
Conclusions ANA detection using automated IIF-HEp-2 interpretation systems is a most useful screening test in SLE. Solid-phase immunoassay methods (ELISA and BioPlex 2200) should be used as confirmatory tests to detect antigen-specific ANA.
Disclosure of Interest None declared