Immunoluminometric Assay for the Midregion of Pro-Atrial Natriuretic Peptide in Human Plasma

The prohormone of atrial natriuretic peptide (proANP) is a polypeptide of 126 amino acids. Mature atrial natriuretic peptide (ANP) consists of amino acids 99–126 and comprises 98% of the natriuretic peptides in the circulation (1). The N-terminal portion of proANP, termed proANP1–98 or NT-proANP, has a much longer half-life than mature ANP and has therefore been suggested to be a more reliable analyte for measurement than mature ANP (2). In addition to other established indications, proANP has recently gained much interest as a potential new marker in the field of sepsis (3), emphasizing the need for a reliable assay for this molecule. All sandwich immunoassays developed for proANP to date use an antibody against the N-terminal region of proANP1–98 combined with a second antibody against either the midregion (4) or C-terminal region (5)(6). However, under certain conditions, the N-terminal region might be minimally accessible for antibody binding (7)(8). Despite the described long half-life of proANP, results from various competitive immunoassays as well as HPLC analyses indicate that proANP1–98 can be subject to further fragmentation (9)(10). We developed a new sandwich immunoassay for midregional proANP (amino acids 53–90; Fig. 1A⇓ ). With this assay, which was named B.R.A.H.M.S SERISTRA® (B.R.A.H.M.S AG), we measured proANP values in 325 healthy controls. EDTA-plasma samples were collected at a blood bank (Red Cross) from 325 consecutive healthy blood donors (age range, 18–67 years; 52.9% male) without clinical evidence of acute disease or a history of chronic illness. Blood donors with risk factors for heart failure were not enrolled in the study. Written consent was obtained from …