QUANTIFICATION OF LIPOPROTEIN(A) PARTICLES CONTAINING VARIOUS APOLIPOPROTEIN(A) ISOFORMS BY A MONOCLONAL ANTI-APO(A) CAPTURE ANTIBODY AND APOLYCLONAL ANTI-APOLIPOPROTEIN-B DETECTION ANTIBODY SANDWICH ENZYME-IMMUNOASSAY

A quantitative sandwich ELISA for lipoprotein(a) [Lp(a)], utilizing a monoclonal capture antibody that recognizes human and rhesus monkey ap olipoprotein(a) [apo(a)] isoforms in combination with a polyclonal ant i-apolipoprotein B-peroxidase conjugate was developed. This assay gene rates a linear calibration curve from 31.2 to 1000 mg/L, is highly rep roducible (intra- and interassay CV of <5% and less-than-or-equal-to 1 2%, respectively), and shows no interference from plasminogen (1 g/L), low-density lipoprotein (6.00 g/L), triglycerides (27.00 g/L from chy lomicrons and 10.00 g/L from very-low-density lipoprotein), hemoglobin (5 g/L), or bilirubin (30 mg/L). This assay format quantifies the con centration of Lp(a) on an equal molar basis regardless of apo(a) isofo rm. In contrast, a commercially available ELISA [Macra Lp(a)] method w ith a monoclonal anti-apo(a) capture antibody and a polyclonal anti-ap o(a) conjugate was found to underestimate the Lp(a) concentrations of individuals with lower-M(r) apo(a) isoforms-whether quantifying the Lp (a) in plasma or the purified lipoprotein. This demonstrates the impor tance of assay format selection in quantifying Lp(a).