186 - Accuratezza diagnostica dei metodi immunoenzimatici per il dosaggio degli anticorpi anti-cromatina (nucleosomi): l’importanza della sorgente antigenica e della definizione del valore soglia

D. Villalta, R. Tozzoli, N. Bizzaro, E. Tonutti, A. Ghirardello, A. Doria Diagnostic accuracy of immunoassays for antichromatin (nucleosome) detection: the relevance of autoantigen source and of the cut off definition. Background. In the last few years, several reports have shown that chromatin (nucleosome) represents the main autoantigen-immunogen in systemic lupus erythematosus (SLE), and that specific antibodies are an important marker of the disease. Methods. To verify the clinical sensitivity and specificity of anti-nucleosome autoantibodies (ANuA), three different ELISA immunoassay methods using different autoantigen preparations were evaluated (1. Quanta-Lite Chromatin, Inova Diagnostics, San Diego, CA; 2. Medizym Antinucleo, Medipan Diagnostica, Selchow, Germany; 3. Nucleosome IgG Elisa, D-tek, Wavre, Belgium), and the results were compared with those obtained with two ELISA assays for anti-nDNA antibody determination (Axis- Shield, Dundee, UK and EliA dsDNA, Pharmacia Diagnostics, Freiburg, Germany). Sera from 321 patients were tested: 101 SLE, 48 infectious diseases, 73 autoimmune rheumatic diseases (20 rheumatoid arthritis, 30 systemic sclerosis and 23 Sjögren’s syndrome) and 99 healthy subjects. Results. Using the cut-off recommended by the manufacturers, the sensitivity for the three kits was 69%, 78% and 74%, and the specificity was 100%, 94.6% and 95.0%, respectively. Using the cut-off corresponding to 95% specificity, the sensitivity of the methods for the ANuA assay was 86%, 77% and 74%, i.e. higher values than those obtained with the two ELISA methods for anti-nDNA (65% and 64%).