Enzyme-linked immunosorbent assay of lipoprotein(a) in serum and cord blood.

We have developed a new sensitive method for quantifying lipoprotein(a) (Lp(a] in human serum, using a 'sandwich' type noncompetitive enzyme-linked immunosorbent assay (ELISA). The solid-phase used was a polystyrene plate. The anti-Lp(a) antibody-enzyme conjugate was labelled by linking Fab' fragments to peroxidase (EC 1.11.1.7) by the maleimide method. The minimum detectable concentration was 0.5 ng/well. Routinely, the assay was carried out with 1,000-fold diluted serum, and Lp(a) was quantified between 4.0 and 500 mg/l. Within-run coefficients of variation (CVs) ranged from 3.5% to 10.4% and between-run CVs from 5.0% to 11.1%. Results by the ELISA were in good agreement with those by radial immunodiffusion (r = 0.955). The distribution of Lp(a) in serum from 820 healthy donors was highly skewed: mean 141.1 mg/l, medium 97.9 mg/l. In cord blood, the mean and median were 15.6 and 9.8 mg/l, respectively. This ELISA for Lp(a) has the advantages of being highly sensitive and specific, simple to perform, and does not use radioisotopes.