Autoantibody testing for connective tissue diseases. Comparison of immunodiffusion, immunoblot, and enzyme immunoassay.

We evaluated 500 consecutive patient serum samples for the presence of six autoantibodies by three antibody detection methods: immunodiffusion, immunoblot, and enzyme immunoassay. Clinical data were reviewed for each patient with positive antibody test results. Serum samples from 60 patients revealed antibodies to Sm, ribonucleoprotein (RNP), SSA/Ro, SSB/La, Scl-70, or Jo-1. There were 7 false-positive test results (1%). All three methods detected autoantibodies in 36 (68%) of 53 patients with connective tissue disease. Immunoblot was the most sensitive method to detect autoantibodies (92%). Enzyme immunoassay and immunodiffusion were less sensitive (81% and 74%, respectively). Antiribonucleoprotein and anti-SSB/La antibodies were more often detected by immunoblotting, whereas anti-SSA/Ro antibodies were more often detected by enzyme immunoassay. Newer antibody detection methods (immunoblot and enzyme immunoassay) are less time consuming than immunodiffusion and show good interassay sensitivity without loss of specificity. A combination of immunoblot and enzyme immunoassay yielded excellent assay sensitivity (100%) and specificity (99%) for detection of autoantibodies.