FRAMINGHAM, MASSACHUSETTS. Natriuretic peptides are cardiac hormones with diuretic, natriuretic, and vasodilatory properties. Atrial natriuretic peptide (ANP) and its N-terminal prohormone (NT-ANP) are produced in the atria, whereas brain natriuretic peptide (BNP) is produced in the ventricles. Both hormones are produced in response to stretching of the walls of the heart. Higher than normal levels of these hormones are found in patients with heart failure and left ventricular dysfunction (low ejection fraction). Clinicians have long attempted to use blood levels of ANP and BNP as a means of diagnosing congestive heart failure and left ventricular dysfunction. However, this approach has, so far, not been very successful because of the lack of data required to establish normal reference ranges. Now researchers at the Harvard Medical School and the Massachusetts General Hospital have overcome this problem. The researchers evaluated 911 healthy subjects (342 men and 569 women) with an average age of 55 years. All had fasting blood samples drawn and analyzed for NT-ANP and BNP.
The researchers found that women had markedly higher levels of natriuretic peptides than did men. Older people also had significantly higher levels than younger people. A 10-year increase in age was associated with a 1.4-fold increase in BNP levels and a 1.2-fold increase in NT-ANP levels. A high diastolic blood pressure was associated with lower BNP and NT-ANP levels as was a higher body mass index. A large left atrium, on the other hand, was associated with higher BNP and NT-ANP levels.
The researchers propose upper (97.5th percentile) limits above which left ventricular dysfunction or heart failure should be suspected. Examples are:
The researchers caution that natriuretic peptide levels above these reference levels do not necessarily imply
that heart failure or ventricular dysfunction is present. Other conditions such as hypertension and renal
failure can also cause abnormally high natriuretic peptide levels.