SULM – Schweizerische Union für Labormedizin | Union Suisse de Médecine de Laboratoire | Swiss Union of Laboratory Medicine

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D Burki1 , M Szemberski1 , L Matter1

1Viollier AG, Immunology, 4002 Basel

Background: Indirect immunofluorescence (IIF) is commonly used to detect ANA. The use of automated Enzyme Immuno Assay (EIA) techniques may substantially reduce both labour and time to result.
Methods: 284 patients were tested for ANA by IIF on HEp-2 cells (ANA HEp-2 Actin, INOVA, San Diego, USA) and by EIA (Quanta Lite ANA, INOVA). Reactive and discrepant samples were tested for antibodies to extractable nuclear antigens (ENA) using a line immuno assay (LIA; Innolia ANA update, Innogenetics, Gent, Belgium). In addition, a panel of sera with known autoantibodies was tested by EIA.
Results: Of 284 sera, 228 were negative and 11 found positive by both IIF (titre �) and EIA. 16 were positive by EIA only, of which 3 were ENA positive. Of 23 IIF indeterminate (titre 80) sera, 14 were EIA positive (of which 2 were ENA positive) and 9 were EIA negative (all ENA negative). 6 were found positive in IIF only (all ENA negative).
Assigning presence of ANA/ENA on the basis of IIF and LIA, sensitivity of EIA was 94.4% (CI95 70.6 – 99.7 %), specificity 91.0 % (86.7 – 94.0%).
From a panel with known reactivities, EIA detected 16/16 centromere, 10/10 SSA, 3/3 SSB, 2/2 Scl-70, 4/9 nucleolar, 1/1 actin, 11/12 mitochondria and 3/7 nuclear dot antibodies.
Discussion: Prevalence of ANA was low (6.3 %). EIA detected 16 of 17 cases of ANA while missing one case of ANA (IIF 1:160, RNP-A). EIA detected 3 cases with ANA (2 Scl70, 1 Histone) which were negative by IIF.
35 of 40 known autoantibodies related to rheumatic disease were correctly identified by EIA, missing 5 of 9 cases with nucleolar antibodies. Of 20 antibodies associated with hepatic disease, 15 were correctly identified by EIA while missing 1/12 mitochondria and 4 of 7 nuclear dot antibodies.
Conclusion: EIA shows promising characteristics for the detection of ANA and a potential to reduce the workload in a setting of low prevalence of ANA. Further studies are required to establish its use in routine analysis.

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