BNP and NT-proBNP

What is BNP?

BNP is a hormone and plays an important role in the regulation of water-salt balance and blood pressure. BNP or its precursor is produced primarily by muscle cells in the ventricles of the heart. In addition, the adrenal glands and the brain also produce BNP, but only in small quantities.

The abbreviation BNP stands for “Brain Natriuretic Peptide”. The English word for brain refers to the fact that scientists first discovered the hormonally active protein in the brains of pigs. “Natriuretic” means that BNP increases the excretion of sodium in the urine.

BNP is now also known by the more appropriate name “B-type natriuretic peptide”.

NT-proBNP

Like BNP itself, this is suitable for assessing cardiac insufficiency (heart failure). In fact, physicians usually prefer NT-proBNP because it has practical advantages: It is more stable and thus remains in the blood longer than active BNP. This makes NT-proBNP easier to detect. However, it is more dependent on age and renal function than BNP.

The BNP value and the NT-proBNP value are not directly comparable! In fact, some factors influence NT-proBNP more than BNP. This is true for renal impairment, for example.

Natriuretic peptides

There are other natriuretic peptides (peptide = small protein) besides BNP. ANP (atrial natriuretic peptide) is particularly important. Like BNP, it is produced mainly by cardiac muscle cells and initially in the form of a precursor. And it is also involved in the regulation of water-salt balance.

When to determine BNP and NT-proBNP?

Heart failure: BNP and NT-proBNP help to diagnose or exclude heart failure, to monitor the course and therapy of the disease and to assess the prognosis.
Chest pain plus shortness of breath: Here, BNP and NT-proBNP (and other parameters) provide clues as to whether the cause lies with the heart or in the lungs (normal measured values = rather no heart-related cause).
Angina pectoris and myocardial infarction: physicians use the measured values of BNP and NT-proBNP, among others, to assess the prognosis in angina pectoris, acute myocardial infarction and after a myocardial infarction.
Assessment of heart failure risk: In patients at risk of cardiovascular disease (e.g. diabetes), measurement of BNP or NT-proBNP helps to detect declining cardiac output at an early stage.
Pulmonary embolism: It can result in right heart failure. Parameters such as BNP or NT-proBNP allow to better assess the risk of such a complication and the prognosis.
potentially heart-damaging drugs: BNP or NT-proBNP measurement is used to monitor therapy. Potentially heart-damaging drugs include anthracyclines and trastuzumab (used in cancer therapy).

BNP and NT-proBNP: Normal values

A BNP of less than 35 pg/ml and a NT-proBNP of less than 125 pg/ml are generally considered normal in the sense of: There is most likely no heart failure.

Doctors suspect heart failure if a patient shows the typical symptoms of shortness of breath (dyspnea), fatigue and water retention (edema), for example in the legs. If these symptoms occur within a short period of time, the cause could be acute cardiac insufficiency. A physician can assess whether this is actually the case by measuring BNP and/or NT-proBNP:

Measured values

Meaning

BNP < 100 pg/ml or

NT-proBNP < 300 pg/ml

acute heart failure very unlikely

BNP ≥ 100 pg/ml or

NT-proBNP ≥ 300 pg/ml

Acute heart failure probable

Measured values

Meaning

BNP < 35 pg/ml or

NT-proBNP < 125 pg/ml

chronic heart failure very unlikely

BNP ≥ 35 pg/ml or

NT-proBNP ≥ 125 pg/ml

Chronic heart failure possible

Heart failure cannot be diagnosed on the basis of BNP/NT-proBNP readings alone! Further examinations are necessary for this (above all a cardiac ultrasound). The above values are also guideline values according to the European Society of Cardiology. Various factors (e.g. gender) influence the limit values for the respective patient (see below).

When interpreting the measured values, physicians must take into account that in addition to a weakened heart muscle, many other factors also influence the blood levels of BNP and NT-proBNP. For example, the BNP and NT-proBNP standard values depend, among other things, on the age and sex of the patient: They increase with years of life and are generally higher in women than in men.

The following table provides an orientation to NT-proBNP standard values (normal values) in pg/ml:

Age	female	male
up to 2 days	321 – 11.987 pg/ml
3 to 11 days	263 – 5.918 pg/ml
12 days to 12 months	37 – 646 pg/ml
1 to 3 years	< 320 pg/ml
4 to 6 years	< 190 pg/ml
7 to 9 years	< 145 pg/ml
10 years	< 112 pg/ml
11 years	< 317 pg/ml
12 years	< 186 pg/ml
13 years	< 370 pg/ml
14 years	< 363 pg/ml
15 years	< 217 pg/ml
16 years	< 206 pg/ml
17 years	< 135 pg/ml
18 to 44 years	< 130 pg/ml	< 86 pg/ml
45 to 54 years	< 249 pg/ml	< 121 pg/ml
55 to 64 years	< 287 pg/ml	< 210 pg/ml
65 to 74 years	< 301 pg/ml	< 376 pg/ml
from 75 years	< 738 pg/ml	< 486 pg/ml

The measured value for BNP and NT-proBNP can also be expressed in the unit nanogram per liter (ng/l) instead of picogram per milliliter (pg/ml). The values correspond to each other, that is, 1 ng/l = 1 pg/ml.

Severity and prognosis in heart failure

These laboratory values are also useful for assessing a patient’s prognosis. If NT-proBNP decreases over time in heart failure patients, this indicates a decreasing risk of cardiovascular complications.

When are BNP and NT-proBNP elevated?

When BNP and NT-proBNP are increased in the blood, in many cases it is due to heart failure. A look at the release and action of the hormone explains why:

Release when pressure rises

When the pressure in the heart rises, the heart muscle cells release the natriuretic hormones BNP and ANP (each as a precursor, which then gives rise to the active hormones). Both hormones cause the kidneys to excrete more sodium and water (natriuretic and diuretic effect). This reduces the blood volume – blood pressure drops, which relieves the heart.

Pressure increase in weak heart

The increase in pressure in the heart can have various causes. Sometimes a particularly large amount of blood in the bloodstream or very high blood pressure is responsible. However, the pressure in the heart also rises when the heart is weak:

The strength of a weakened heart muscle is not sufficient to pump blood efficiently through the body. As a result, it backs up in the heart. This causes the pressure to rise, whereupon the heart muscle cells release BNP and ANP.

When is BNP or NT-proBNP decreased?

BNP and NT-proBNP cannot be too low (there is no lower limit). However, some factors can cause the readings to be lower than normal.

This is the case, for example, if you are very overweight (obesity) – as well as during therapy with ACE inhibitors and diuretics. Physicians prescribe both groups of active ingredients for chronic heart failure and high blood pressure, among other things.

In patients taking ARNI, the NT-proBNP value is suitable for monitoring progress – but not the BNP value, because this increases due to the drug. The currently available ARNI is sacubitril/valsartan.

BNP/NT-proBNP value too high: What to do?

If heart failure is a possible or probable explanation for BNP and/or NT-proBNP being elevated, the physician will perform further tests. They are necessary to confirm the suspicion of heart failure. A heart ultrasound examination (echocardiography) is particularly important. If the diagnosis of heart failure is then established, the physician initiates appropriate therapy.

Other pathological causes of BNP or NT-proBNP elevation (e.g., renal impairment) must also be treated appropriately as soon as the diagnosis is confirmed.

Also, ask your health care provider what you can do to help your health if you have elevated BNP/NT-proBNP levels.