Antibody tests are blood tests that determine specific antibodies which simplify the diagnosis of lupus, Antinuclear antibody (ANA) Anti-RNP. Anti-Smith (Sm),.Anti-Smith antibodies are present in some cases of systemic lupus erythematosus (SLE) and mixed connective-tissue disease (MCTD). Smith antigens are elements of the extractable nuclear antigens (ENAs); typically they are the proteins that are resistant to ribonuclease.