An immunoluminometric assay for N-terminal pro-brain natriuretic peptide: development of a test for left ventricular dysfunction

Measurement of plasma levels of brain natriuretic peptide (BNP) has been us ed to assess left ventricular dysfunction and prognosis. Levels of the N-te rminus of the precursor of BNP (NT-proBNP) have been reported to be elevate d to a greater extent than BNP in left ventricular dysfunction. We have dev ised a non-radioactive sensitive and specific assay for NT-proBNP based on a competitive ligand binding principle. The chemiluminescent label 4-(2-suc cinimidyl-oxycarbonylethyl)phenyl-10-methylacridinium 9-carboxylate fluoros ulphonate was used to label peptides representing domains in the middle and C-terminal sections of NT-proBNP. Assay of the C-terminal section of NT-pr oBNP (amino acids 65-76) in patients with proven left ventricular dysfuncti on [left ventricular wall motion index median 0.9 (range 0.3-1.4)] revealed elevated values [median 639 (386-911) fmol/ml] compared with normal contro ls [left ventricular wall motion index of 2 in all, NT-proBNP median 159 (1 20-245) fmol/ml, P < 0.001]. Measurement of the middle section of NT-proBNP (amino acids 37-49) was not a discriminating test. It is thus possible to derivatize small peptides with a methyl acridinium label and preserve immun odetection with specific antibodies. Such methodology may allow non-radioac tive immunoluminometric assays to be devised.