Electroimmunoassay and radioimmunoassay for the quantitation of high density apolipoproteins A-I and A-II.

An electroimmunodiffusion assay (EID) for the quantitative determination of the major apolipoproteins of the human high density lipoprotein fraction, apolipoproteins A-I and A-II, was compared with a solid phase radioimmunoassay (RIA), previously described by us. Data obtained by both methods largely depended on the pretreatment of the sera. Pretreatment consisted either of delipidation with an ether/ethanol mixture or tetramethyl urea, or of denaturation by heating the sera to 52 degree C for 3 hours. Delipidation with ether/ethanol produced a decrease of apolipoprotein A-I values in both methods as compared to treatment with tetramethyl urea. In contrast, the ether/ethanol treatment did not alter apolipoprotein A-II values in the RIA, while in the EID this procedure led to an increase of apolipoprotein A-II values. Heating gave an increase of both apolipoproteins A-I and A-II in both assays, but results obtained by EID were difficult to interpret because of the appearance of indistinct or double rockets. Comparable results by both methods were obtained, when sera were pretreated with tetramethyl urea. Handling and reproducibility seemed to be slightly better with the EID than with the RIA.