COMPARISON OF 3 COMMERCIALLY AVAILABLE ENZYME IMMUNOASSAYS FOR THE SCREENING OF AUTOANTIBODIES TO EXTRACTABLE NUCLEAR ANTIGENS

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 be en classically performed by double immunodiffusion. Testing large numb ers of clinical specimens for autoantibodies to ENA by double diffusio n techniques can be time-consuming and expensive. ENA screening system s that employ enzyme immunoassay (EIA) technology have recently become commercially available. We compared three EIA ENA assays to classic O uchterlony double diffusion techniques. Furthermore, the sensitivity o f each antigen and methodology (including ANA immunofluorescence using HEp-2 cells) was tested using ENA positive sera possessing single aut oantibodies. Two of the three EIAs that detected immunoglobulin G type autoantibodies to Smith (Sm), ribonucleoprotein (RNP), Sjogren's synd rome-associated antigens Ro (SSA) and La (SSB), were provided by INOVA and Sigma Diagnostics. A third EIA, which also included scleroderma-a ssociated antigen 70 (SCL-70/DNA-topoisomerase 1) and histidyl-tRNA sy nthetase (JO-1) in addition to the four previously stated antigens, wa s provided by Clark Laboratories. This latter ENA screen detected IgG, IgA, and IgM type autoantibodies. Included in the study were sera cov ering a wide variety of anti-nuclear and other autoantibodies. Sensiti vity was 100% for all EIA ENA screens when compared to Ouchterlony dou ble diffusion and specificity exceeded 95% in each case. Sensitivity s tudies showed Ouchterlony to be less sensitive than EIA when detecting low levels of autoantibodies to ENA. After the detection of ANA antib ody by IFA, EIAs utilizing combined antigens can be used to screen lar ge numbers of clinical specimens for autoantibodies against SSA, SSB, Sm, RNP/SCL-70, and Jo-1 prior to confirmation by Ouchterlony double d iffusion. (C) 1995 Wiley-Liss, Inc.