Detecting Autoantibodies to Small Nuclear Ribonucleoproteins: Comparison of Three Methods

Three techniques were compared for the analysis of autoantibodies to two small nuclear ribonucleoproteins (snRNPs): the Smith antigen (Sm) and ribonucleoprotein (RNP). Hemagglutination, immunodiffusion, and immunoblotting methods were used to analyze serum specimens from 5,000 patients for autoantibodies to extractable nuclear antigen (ENA), Sm, RNP, and small nuclear ribonucleoprotein (snRNP) polypeptides. Hemagglutination was the most sensitive test of the three, showing positive results in 510 (10%) specimens. The three methods showed good correlation, with some exceptions. Immunoblotting was a sensitive, specific method for detecting autoantibodies to specific snRNP polypeptides. The immunodiffusion test was less sensitive and may not detect low-titer autoantibodies to the Sm antigen. Although the hemagglutination test was extremely sensitive, the specificity of anti-ENA antibodies often cannot be determined when the titer is less than 1:128.