Detection of antibody against extractable nuclear antigen by an enzyme-linked immuno-sorbent assay. Results from patients with rheumatic and internal medical diseases.

Anti-ENA antibody determination by ELISA technique may offer a valuable diagnostic help in the discrimination of patients with mixed connective tissue disease (MCTD) from those with other chronic inflammatory connective tissue diseases. Determination of this antibody was performed in a prospective designed investigation among 101 blood donors, 154 patients with various non-rheumatic internal medical diseases, and 229 patients with chronic inflammatory connective tissue diseases, including five patients with MCTD. A positive titre of anti-ENA antibody was found in approximately 10% of blood donors and patients with various internal medical disorders. A highly positive anti-ribonucleoprotein (RNP) titre was found in the patients with MCTD, but was also observed in patients with other chronic inflammatory connective tissue diseases, giving a predictive value of 56% for MCTD. We conclude that highly positive anti-RNP antibody values do not automatically indicate the diagnosis MCTD. Other diagnostic possibilities should still be considered.