Improvement in diagnosis of rheumatoid arthritis using dual indirect immunofluorescence and immunoblotting assays for antifilaggrin autoantibodies: a retrospective 3 year study

To determine the clinical usefulness of measuring antistratum corneum (ASC) and antifilaggrin autoantibodies (AFA) to discriminate between rheumatoid arthritis (RA) and other rheumatic or autoimmune diseases, using an indirect immunofluorescence (IIF) assay, along with a complementary immunoblotting technique (IB) when IIF detection of ASC was negative.Sera from 346 patients were studied: 189 sera from patients with RA seen in the same clinic, 92 from patients with non-RA rheumatic diseases, 24 from nonrheumatic autoimmune diseases, and 41 from healthy blood donors. ASC and AFA were detected using IIF and IB, respectively.ASC detection using IIF showed a specificity of 97.5% for RA with 44.4% sensitivity. When both IIF and IB techniques were used, sensitivity for RA increased significantly (up to 53.4%; p0.01) with no decrease in specificity (p0.01).These data confirm the usefulness of 2 different techniques performed simultaneously for detecting ASC/AFA, and the usefulness of these biological markers for discriminating between RA and other rheumatic diseases in clinical practice.