Brain natriuretic peptide (BNP), also known as B-type natriuretic peptide (also BNP) or GC-B, is a 32 amino acid polypeptide secreted by the ventricles of the heart in response to excessive stretching of heart muscle cells (cardiomyocytes). BNP is named as such because it was originally identified in extracts of porcine brain, although in humans it is produced mainly in the cardiac ventricles.

BNP is co-secreted along with a 76 amino acid N-terminal fragment (NT-proBNP) which is biologically inactive. BNP binds to and activates the atrial natriuretic factor receptors NPRA, and to a lesser extent NPRB, in a fashion similar to atrial natriuretic peptide (ANP) but with 10-fold lower affinity. The biological half-life of BNP, however, is twice as long as that of ANP, and that of NT-proBNP is even longer, making these peptides better targets than ANP for diagnostic blood testing.

The physiologic actions of BNP are similar to ANP and include decrease in systemic vascular resistance and central venous pressure as well as an increase in natriuresis. Thus, the net effect of BNP and ANP is an increase in cardiac output and a decrease in blood volume.

Clinical significance

Both BNP and NT-proBNP levels in the blood are used for diagnosis of acute congestive heart failure (CHF) and may be useful to establish prognosis in heart failure, as both markers are typically higher in patients with worse outcome.^[1] The plasma concentrations of both BNP and NT-proBNP are also typically increased in patients with asymptomatic or symptomatic left ventricular dysfunction.

There is no level of BNP that perfectly separates patients with and without heart failure ^[2]. BNP and NT-proBNP tests have high sensitivity but rather low specificity, meaning that low values are accurate at excluding heart failure as a diagnosis, but high values are not conclusive in identifying heart failure.

BNP < 100 pg per milliliter

• sensitivity = 90%
• specificity = 76%

BNP < 50 pg per milliliter

• sensitivity = 97%
• specificity = 62%

For patients with CHF, BNP values will generally be above 100 pg per milliliter; however, a more conservative interpretation of the BNP is that normal values are less than 50 pg per milliliter in order to achieve adequate sensitivity. There is a diagnostic 'gray area', often defined as between 100 and 500 pg/mL, for which the test is considered inconclusive. Values above 500 pg/mL are generally considered to be positive.

BNP can also be elevated in renal failure (as BNP is excreted renally) and it can be decreased in obesity.

BNP is also marketed as nesiritide for the treatment of acute decompensated congestive heart failure ^[4].

References

Further reading

External links

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