Anti-U1 ribonucleoprotein antibody positivity 2020-06-13T11:09:23Z The presence autoantibodies in the serum that react to proteins (70 Kd, A, C) that are associated with U1 RNA and form U1snRNP. Anti-RNP-antibodies Anti-U1-RNP antibody positivity High titers of anti-RNP antibodies are diagnostic of mixed connective tissue disorder (MCTD). Anti-RNP antibodies can also be found in patients with systemic lupus erythematosus. Anti-Scl-34 antibody positivity Anti-U3 ribonucleoprotein antibody positivity Extractable nuclear antigen positivity