Evaluation and comparison of commercial immunoassay methods for the determination of N-terminal proANP in plasma and atrial cardiac tissue

Abstract: We measured ANP and N-terminal proANP related peptides with competitive and non-competitive immunoassay methods in plasma samples of healthy subjects and patients with cardiac or renal failure, as well as in cardiac tissue samples, in order to compare the analytical performances and clinical usefulness of these assays. N-terminal proANP was assayed with competitive and/or non-competitive enzyme-immunoassay kits: one sandwich non-competitive ELISA and two competitive enzyme-imunoassay EIA methods; ANP was measured with an IRMA method. Three groups of subjects were studied: 67 healthy volunteers, 61 patients with different degrees of cardiac failure, and 51 patients with renal failure undergoing chronic hemodialysis. Atrial tissues were obtained from the right auricle in 15 patients during an aortocoronary bypass operation. Cardiac tissue from two subjects, collected during autopsy, was also assayed. The values found with the immunoassay methods for N-terminal proANP in normal subjects and patients were highly correlated; however, the ELISA kit was able to separate the group of normal subjects from the two groups of patients with cardiac or renal failure more efficiently than the other immunoassay methods. Furthermore, ELISA proANP and IRMA ANP showed similar results in samples of atrial tissue extracts of patients who had undergone an aorto-coronary bypass operation, while the two competitive EIA methods showed higher values. Our study suggests that competitive (EIA) and noncompetitive (ELISA) immunoassays for N-terminal proANP assay show different analytical performances and measure, at least in part, different substances. Our data also indicate that the ELISA method is more suitable than the competitive EIA methods for the determination of the intact N-terminal proANP(1-98) in plasma samples of patients with heart or renal failure and in cardiac tissue extracts.