Comparison of three commercially available enzyme immunoassays for the screening of autoantibodies to extractable nuclear antigens

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Abstract
The initial screening test used in the diagnosis of connective tissue diseases is based on the detection of antinuclear antibodies (ANA) by indirect immunofluorescence (IFA). When the ANA screen is positive, it is often useful to determine the specificity of the autoantibody to a series of extractable nuclear antigens (ENA), a procedure that has been classically performed by double immunodiffusion. Testing large numbers of clinical specimens for autoantibodies to ENA by double diffusion techniques can be time‐consuming and expensive. ENA screening systems that employ enzyme immunoassay (EIA) technology have recently become commercially available. We compared three EIA ENA assays to classic Ouchterlony double diffusion techniques. Furthermore, the sensitivity of each antigen and methodology (including ANA immunofluorescence using HEp‐2 cells) was tested using ENA positive sera possessing single autoantibodies. Two of the three EIAs that detected immunoglobulin G type autoantibodies to Smith (Sm), ribonucleoprotein (RNP), Sjögren's syndrome‐associated antigens Ro (SSA) and La (SSB), were provided by INOVA and Sigma Diagnostics. A third EIA, which also included scleroderma‐associated antigen 70 (SCL‐70/DNA‐topoisomerase I) and histidyl‐tRNA synthetase (Jo‐1) in addition to the four previously stated antigens, was provided by Clark Laboratories. This latter ENA screen detected IgG, IgA, and IgM type autoantibodies. Included in the study were sera covering a wide variety of anti‐nuclear and other autoantibodies. Sensitivity was 100% for all EIA ENA screens when compared to Ouchterlony double diffusion and specificity exceeded 95% in each case. Sensitivity studies showed Ouchterlony to be less sensitive than EIA when detecting low levels of autoantibodies to ENA. After the detection of ANA antibody by IFA, EIAs utilizing combined antigens can be used to screen large numbers of clinical specimens for autoantibodies against SSA, SSB, Sm, RNP/SCL‐70, and Jo‐1 prior to confirmation by Ouchterlony double diffusion.©1995 wiley‐Liss, inc.