Immunoturbidimetric method for routine determinations of apolipoproteins A-I, A-II, and B in normo- and hyperlipemic...

We describe a method for routine immunoturbidimetry of apolipoproteins (apo) A-I, A-II, and B in both normo- and hyperlipemic sera. A special antiserum reagent, consisting of a highly concentrated mixture of nonionic and anionic detergents (final concentration in the assay, 36 g/L), rapidly removes intrinsic turbidities of even strongly lipemic sera without interfering with the antigen-antibody precipitation reaction. The method has good precision, and obviates the need for special sample pretreatment, extended incubation periods, and measurment of sample blanks. A comparison with established immunoephelometric assays generally showed close agreement for analytical recoveries of the three apolipoproteins. However, in samples containing greater than or equal to 18 g of triglycerides per liter, the nephelometric assays yielded about two- to threefold higher values for apo A-II and B than did the turbidimetric procedure. To elucidate this discrepancy, we used the turbidimetric methods to assay sera with and without enzymatic lipolytic pretreatment. Even for samples with triglyceride concentrations up to 60 g/L, complete enzymatic lipolysis (as evidenced by thin-layer chromatography) did not significantly alter the recoveries of apo A-II and B from those obtained with the untreated specimens. Thus the immunoturbidimetric methods yield reliable results for apo A-I, A-II, and B, not only in normo- but also in hyperlipemic sera.