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Reference Notes and Guidelines

Antibodies to Extractable Nuclear Antigens (ENA) are found in patients with mixed connective tissue diseases (MCTD). MCTD describes a mixture of syndromes which include myositis, lupus, rheumatoid arthritis and scleroderma . Together with the titres and patterns of the ANA and the results of the ENA Antibodies and other laboratory tests, as well as the clinical picture, the differentiation of the different connective diseases may be diagnosed.

However, as a general guideline, nRNP/Sm Antibodies are found in 50 % of patients with SLE and also in patients with other MCTD. Other MCTD may be characterized by negative anti-DNA and Sm antibodies. Antibodies to Sm and a high ANA and Anti-DNA test is highly characteristic of SLE. Antibodies to SS-A (Ro) and SSB (La) are found in 40-45% of patients with SjogrenOs syndrome, and in about 20% of patients with SLE and rheumatoid arthritis as well as many other conditions. Scl-70 is a good marker for scleroderma (60%) when the skin is affected. Jo-1 Antibodies occur in 20% of patients with myositis. Please note that testing for ENA antibodies is not useful in patients without a positive ANA titre.