TIME-RESOLVED IMMUNOFLUOROMETRIC ASSAY FOR THE QUANTIFICATION OF LIPOPROTEIN(A) IN SERUM

Although two recent studies have failed to reveal lipoprotein(a) (LP(a )) serum concentrations > 300 mg/l to be an independent risk factor fo r early onset of atherosclerosis, Lp(a) serum concentrations are frequ ently measured to evaluate the additional risk of coronary heart disea se. We describe a time-resolved immunofluorometric assay (TRIFMA) for quantifying Lp(a) levels in human serum using commercially available r eagents, which is rapid, robust and simple to perform. The two-site im munometric assay was based on microtitre plates as solid phase coated with a polycloncal anti Lp(a) antibody. The liquid-phase antibody was labelled with biotin and detected by europium labelled streptavidin in the DELFIA 1232 fluorometer. The measuring range was 2-1600 mg/l. The intra-assay imprecision was < 7% (CV), the inter-assay imprecision < 12% (CV). No interference was detected with plasminogen concentrations up to 2.2 g/l. There was an acceptable correlation with a commerciall y available enzyme immunoassay (r = 0.95) and with electroimmunodiffus ion (r = 0.85) on 100 routine serum samples measured. The assay appear ed to detect different Lp(a) isoforms as dilution curves were parallel for B/F, S-2 and S-4 isoforms.