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 for early onset of atherosclerosis, Lp(a) serum concentrations are frequently measured to evaluate the additional risk of coronary heart disease. We describe a time-resolved immunofluorometric assay (TRIFMA) for quantifying Lp(a) levels in humans serum using commercially available reagents, which is rapid, robust and simple to perform. The two-site immunometric 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 concentration up to 2.2 g/l. There was an acceptable correlation with a commercially available enzyme immunoassay (r = 0.95) and with electroimmunodiffusion (r = 0.85) on 100 routine serum samples measured. The assay appeared to detect different Lp(a) isoforms as dilution curves were parallel for B/F, S2 and S4 isoforms.