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

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 sa mples, in order to compare the analytical performances and clinical usefuln ess 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 a n IRMA method. Three groups of subjects were studied: 67 healthy volunteers , 61 patients with different degrees of cardiac failure, and 51 patients wi th renal failure undergoing chronic hemodialysis. Atrial tissues were obtai ned from the right auricle in 15 patients during an aortocoronary bypass op eration. Cardiac tissue from two subjects, collected during autopsy, was al so assayed. The values found with the immunoassay methods for N-terminal pr oANP in normal subjects and patients were highly correlated; however, the E LISA kit was able to separate the group of normal subjects from the two gro ups of patients with cardiac or renal failure more efficiently than the oth er immunoassay methods. Furthermore, ELISA proANP and IRMA ANP showed simil ar results in samples of atrial tissue extracts of patients who had undergo ne an aorto-coronary bypass operation, while the two competitive EIA method s showed higher values. Our study suggests that competitive (EIA) and nonco mpetitive (ELISA) immunoassays for N-terminal proANP assay show different a nalytical performances and measure, at least in part, different substances. Our data also indicate that the ELISA method is more suitable than the com petitive 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 card iac tissue extracts.