BNP (B-type natriuretic peptide): BNP (B-type natriuretic peptide or brain type natriuretic peptide is a hormone released from the heart in response to stretch, usually due to heart failure. Another related hormone is ANP or atrial natriuretic peptide, which is released from the upper chambers of the heart (atria) in response to stretch.
N-terminal pro-brain natriuretic peptide (NT-proBNP) is related to BNP. In response to stretch of the ventricle, pro-BNP is released. It is cleaved by enzymes into biologically inactive NT-proBNP and biologically active BNP. NT-proBNP has a longer half life and more stable blood levels. Its level indicates the status of heart failure over the previous 12 hours.
What is the role of BNP and NT-proBNP testing in the emergency department?
Elevated blood levels of BNP and NT-proBNP would indicate heart failure as the cause of breathlessness. Vice versa, normal values will probably exclude a cardiac cause for the breathlessness and we have to search for other causes. Point-of-care tests which can be done from the emergency department with reports being available in a short period is very useful for this purpose.
In what other situations can these be tested?
These can be used as a test for heart failure in other locations like outpatient clinic, wards and intensive care units, when in doubt. Mostly it is useful to differentiate between respiratory and cardiac causes of breathlessness. Higher levels also indicate poor outcome.
Can the levels of BNP and NT-proBNP be falsely elevated?
Levels go up as age advances. Hence different age wise cut off levels have been developed for interpretation of test results. Levels can also be very high when there is kidney failure. Hence caution is needed in interpreting the results in the elderly and in those with impaired kidney function.
Can BNP and NT-proBNP levels be divergent while on certain medications?
Yes, the levels can be divergent when one is taking a new class of heart failure medication known as ARNI (Angiotensin II Receptor Blocker Neprilysin Inhibitor). The medication prevents breakdown of BNP and hence levels rise. But it has no effect on NT-proBNP. Hence estimating BNP is not useful while on this new class of medications, while estimating NT-proBNP is still useful.