A competitive ELISA for lipoprotein(a)

A competitive ELISA for lipoprotein(a) (Lp(a)) is described. The method uses a commercially available polyclonal anti-Lp(a) antibody and an IgG biotinstreptavidin-horseradish peroxidase detection system. The method is simple and robust with an assay sensitivity of 0.7 ng/well (1.4 μg/l). The antibody cross-reactivity was 0.14% against LDL and 0.70% against plasminogen. The coefficients of variation obtained with control sera of 266 and 552 mg/l were: 5.0% and 4.6% ( n = 6), respectively for the intraassay; and 10.8% and 9.5% ( n = 16), respectively for the interassay. The method showed an excellent correlation with a commercial immunoradiometric assay (IRMA), y ( ELISA) = 0.94 x ( IRMA) - 8, ( r = 0.98). A recovery study in which a 200 mg/L standard and four plasma samples were diluted with different proportions of a low plasma sample, gave linear relationships and also confirmed the specificity of the antibody.