The Anti-RNP test (anti-ribonucleoprotein antibody) is a specialized blood test used to identify autoantibodies against protein-RNA complexes (ribonucleoproteins) in the cell nucleus. This test is primarily used in the diagnosis of mixed connective tissue disease (MCTD), which combines features of systemic lupus erythematosus (SLE), scleroderma, and polymyositis. Anti-RNP antibodies, especially against U1-snRNP, are found in 95-100% of patients with MCTD, and high levels (high titers) often indicate this disease. However, these antibodies may also be present in other autoimmune diseases such as lupus, scleroderma, polymyositis, and Sjögren’s syndrome, usually at lower titers. Clinical symptoms associated with positive Anti-RNP include Raynaud’s phenomenon, joint inflammation, myositis (muscle inflammation), lung involvement (such as pulmonary hypertension), and hand swelling. The test is typically performed by ELISA or Immunoblot as part of an ENA panel. Interpretation of results should be done alongside clinical evaluation, supplementary tests (such as ANA, anti-Sm), and imaging, as the presence of Anti-RNP alone is not sufficient for a definitive diagnosis. In MCTD, Anti-RNP often appears in isolation (without other ENA antibodies), whereas in lupus it may be present together with anti-Sm or anti-dsDNA. Anti-RNP plays an important role in distinguishing MCTD from other autoimmune diseases and in planning targeted treatment.
