NT-proBNP (B-type natriuretic peptide)

NT-proBNP is a fragment produced when the hormone BNP (B-type natriuretic peptide) is made. Both come mainly from the muscle cells of the heart's ventricles. NT-proBNP is measured in serum, in the test catalogue together with troponin and D-dimers; the blood sample is taken in a practice. In the blood, NT-proBNP is more stable and detectable for longer than active BNP, which is why this value is usually measured.

What NT-proBNP and BNP do in the body

When the ventricles are stretched by too much blood volume or too high a pressure, the muscle cells produce more of the precursor proBNP. It is split into the active hormone BNP and the inactive NT-proBNP, which enter the blood in equal amounts. BNP relieves the heart: it prompts the kidneys to excrete more salt and water, widens the blood vessels and slows down the renin–angiotensin–aldosterone system and the stress system, which would otherwise raise blood pressure and fluid volume. NT-proBNP itself has no known effect, but reflects how strongly the heart is currently being stretched.

Low NT-proBNP – what does it mean?

A low NT-proBNP value is the normal case. It speaks against the ventricles being heavily strained by volume or pressure at the time of the blood sample, and is therefore looked at with shortness of breath to assess heart failure as a cause. In overweight people, studies have observed lower values than the strain on the heart would suggest – presumably because fat tissue breaks down more natriuretic peptides. This is taken into account in the interpretation.

Raised NT-proBNP – what happens in the body?

A raised value shows that the heart walls are being stretched more. This is the case in heart failure, when the heart no longer pumps the blood onwards sufficiently and it backs up in front of the chambers. Heart valve disease, atrial fibrillation, high blood pressure with a thickened heart wall, inflammation of the heart muscle or raised pressure in the pulmonary circulation, for example with a pulmonary embolism, also raise NT-proBNP. Because it is excreted via the kidneys, it is higher with reduced kidney function; it also rises with increasing age. Through BNP the body tries to excrete fluid and relieve the heart.

The interpretation is given in your report.