Evaluation and characterization of EIA measuring autoantibodies against oxidized LDL.

Autoantibodies against oxidized LDL (oxLDL) have been measured in many laboratories. Comparison of data between laboratories is difficult because of methodological variations and differences in the expression of results. We have optimized an enzyme immunoassay (EIA), which measures autoantibodies against oxLDL and evaluated the effect on results of different ways of expressing the data. Optimized conditions were as follows: coating concentration 2 microg/ml of LDL on polysorp plates, 1% human serum albumin (HSA) as a blocking agent, sample dilution 1:50, conjugate dilution 1:8000, and 0.2% HSA in sample and conjugate diluents. The amount of autoantibodies expressed as ratios between oxLDL and native LDL (natLDL), as titers against oxLDL or as differences between binding to oxLDL and natLDL showed significant differences among groups of coronary heart disease (CHD) patients with different diagnosis or treatment procedures. However, there were no differences among the groups when the results were expressed as the ratio between antibody titer against oxLDL and a standard serum (oxLDL/stand). After standardization oxLDL autoantibody test may become a useful tool for analysis of the risk for CHD.