A new, fast and reliable radioimmunoassay of brain natriuretic peptide in human plasma. Reference values in healthy subjects and in patients with different diseases

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Abstract
A new, fast and reliable radioimmunoassay for measurement of brain natriuretic peptide (BNP) in human plasma has been developed and its application is reported in healthy subjects and in patients with congestive heart failure, chronic renal failure, liver cirrhosis and essential hypertension. The antibody was raised in rabbits, the tracer was made by the iodogen method and polyethylene glycol was used for separation of free and bound tracer. BNP was extracted from plasma using Sep-Pak C18 cartridges. The recovery of unlabelled BNP added to plasma was 77.5±6.2% (mean±SD). The detection limit in plasma was 0.55 pmol 1-1. No cross-reactivity existed with the natriuretic peptides ANP, CNP or urodilatin. In 124 healthy subjects the mean BNP was 1.8±1.0 pmol 1-1 (SD), range 0.6–5.5. BNP increased slightly with age, was higher in women than men and had no circadian rhythm. In eight patients with congestive heart failure the median BNP level was 30.5 pmol 1-1, range 3.9–65.3. In 14 patients with chronic renal failure the median BNP level was 50.5 pmol 1-1, range 10.9–219.8 before dialysis, and 38.0 pmol 1-1, range 9.4–180.0 immediately following dialysis. In 25 patients with liver cirrhosis the median BNP value was 7.8 pmol 1-1, range 1.2–43.1. There was no difference between patients with or without ascites. In 18 medically treated patients with essential hypertension the median BNP level was 5.0 pmol 1-1, range 1.2–45.5 pmol 1-1.