Sensitivity and specificity of autoantibody tests in the differential diagnosis of lupus nephritis.

Several studies have investigated the potential of various autoantibody tests in the diagnosis of systemic lupus erythematosus (SLE). Many lupus patients initially present with glomerulonephritis. In that clinical situation the main differential diagnosis are other forms of glomerulonephritis. In this study the diagnostic value of nine test kits for autoantibody against ANA, dsDNA, circulating immune complexes, C1q, nucleosomes, histones and Sm as well as C3 and C4 levels was evaluated in 39 patients with biopsy-proven lupus nephritis in comparison to 43 patients suffering from other forms of glomerulonephritis. The most useful test was an anti-nucleosome antibody enzyme-linked immunosorbent assay (ELISA) with a sensitivity of 90% and a specificity of 88%. All tests for anti-dsDNA antibodies (Crithidia luciliae Anti-dsDNA, BINDAZYME Anti-dsDNA, FARRZYME high avidity Anti-dsDNA) were of moderate sensitivity and very good specificity. Decreasing the cut-off for the conventional anti-dsDNA ELISA (BINDAZYME) considerably increased its sensitivity (87%) without loss of specificity (90%). Tests for anti-C1q and immune complexes performed worse than the antidsDNA tests. As anti-histone and Sm antibodies are present only in a minority of lupus nephritis patients they are of limited value in diagnosing the disease. In conclusion, testing for anti-nucleosome antibodies and the conventional anti-dsDNA ELISA with lower cut-off provide the best diagnostic aids for differentiation of lupus nephritis from other forms of glomerulonephritis.