Radioimmunoassays for plasma C-type natriuretic peptide determination: a methodological evaluation

C-Type natriuretic peptide (CNP) is a member of the family of natriuretic peptides with vasodilatory properties, and is produced and secreted by endothelial cells. It seems to play a central role in the paracrine vasomotor control of tone and to be important in several clinical conditions characterized by endothelial dysfunction. We evaluated the analytical performance of a commercially available radioimmunoassay for CNP after a preliminary extraction with Sep-Pak C18. Its analytical reliability was checked by determination of CNP plasma levels in healthy subjects (n = 23) and in patients with different diseases, likely characterized by endothelial dysfunction, such as chronic heart failure (n = 133) and cirrhosis (n = 84). The extraction yield was 78+/-3%. Accuracy of the radiommunological determination was evaluated by dilution (45-370 microL of extracted plasma) and recovery tests (>80%). Between- and within-assay variabilities were < or = 10% and analytical sensitivity was 0.41+/-0.015 pg/tube. Plasma CNP in patients with chronic heart failure and with cirrhosis was significantly raised compared to controls (p<0.0001 and p = 0.001, respectively). The sensitivity, accuracy and variability levels of the method proposed for CNP assay was suitable for reliable detection of changes in CNP plasma levels in the clinical setting.