BNP in Heart Failure

Heart failure
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BNP in Heart Failure

Q. My husband has had heart failure on and off for the past two years. Sometimes when he needs to go in for treatment, his doctor will mention his "BNP levels" as if they're something we should be worried about. I have never gotten a clear explanation of what these BNP levels are, or what we should be doing about them. Can you explain them?

Answer:

BNP refers to "brain natriuretic peptide," a hormone that helps regulate the body's salt and water content, as well as blood pressure.

While BNP was first identified in brain tissue (hence the name), it turns out to be chiefly produced by the heart.

BNP is released into the blood circulation by heart muscle cells whenever the pressures within the heart become too high. BNP causes the kidneys to excrete salt and water, and also reduces blood pressure — actions that all tend to bring the high cardiac pressures back down toward normal. 

As your doctor may have told you, heart failure — especially when accompanied by an acute episode of severe dyspnea (breathlessness) — is almost always accompanied by elevated cardiac pressures, which will cause heart cells to release BNP. So, when people experience acute worsening of heart failure, their BNP levels typically become very high.

This means that measuring BNP levels can help the doctor tell whether a patient's dyspnea is due to heart failure or something else (for instance, chronic obstructive lung disease or a pulmonary embolus).

Greatly elevated BNP levels usually indicates that cardiac pressures are significantly elevated — which means that heart failure is very likely to be present. 

However, we should keep in mind that, while elevated BNP levels are considered a bad thing (because it indicates that heart failure is probably going on), the BNP elevation itself is not “bad,” because it represents the body’s attempt to self-correct one of the main problems associated with heart failure (high cardiac pressures).

In fact, for several years BNP, in drug form, was used by cardiologists as a treatment for acute heart failure. (More on this below.)

When Are BNP Levels Measured?

Doctors often will measure the BNP blood levels when someone has acute or worsening dyspnea, and the cause is not quite clear.

This situation is fairly common. Many people who have chronic heart failure also have chronic lung disease (especially if they are smokers), and it can sometimes be quite difficult to tell whether a person is suffering from symptoms of heart failure or symptoms from their lung condition. Measuring BNP levels can be a quick way to figure out which underlying disorder is the culprit.

Measuring BNP can also be helpful in diagnosing heart failure from diastolic dysfunction, a condition that can be missed because cardiac enlargement (a prominent finding with most other kinds of heart failure), is often not present in diastolic heart failure.

What Do BNP Levels Indicate?

In healthy people, BNP levels are usually below 100 pg/ml.

A BNP level above 400 pg/ml means that heart failure is very likely to be the cause of a person’s dyspnea.

BNP levels between 100 and 400 pg/ml are simply not very helpful in determining whether heart failure is the cause of a patient's symptoms.

When BNP levels are in this “intermediate” range, the doctor will have to rely on other diagnostic testing, such as an echocardiogram, to clinch the diagnosis.

Interpreting BNP levels is not always straightforward. People with kidney disease can have elevated BNP levels without any heart failure. Also, older people and women without heart failure tend to have higher BNP levels, and obese individuals (for reasons that are not known) tend to have lower BNP levels. So strict cutoff levels for determining normal vs. abnormal BNP levels are not possible, and the interpretation of this lab result has to be individualized.

Furthermore, the use of serial BNP measurements to guide heart failure therapy has not been shown to be helpful in improving overall results. 

Is BNP Useful As A Heart Failure Treatment?

Several years ago, there was a lot of excitement around the use of BNP itself as a treatment for heart failure. Because BNP is a hormone that reduces the body's salt and water content and lowers blood pressure, researchers thought it might be useful as a heart failure therapy. An intravenous form of BNP was subsequently developed.

This drug, nesiritide (Natrecor), was approved in 2001 by the FDA for the treatment of acute heart failure.

It was used fairly widely in clinical practice for several years, but subsequent randomized clinical trials failed to confirm that this expensive and inconvenient drug significantly improved the outcomes of patients with heart failure. Its usage today is mainly limited to patients who fail to respond adequately to more routine heart failure therapy.

A Word From Verywell

In some circumstances, measuring blood levels of BNP can be helpful in diagnosing whether heart failure is responsible for a person’s symptoms of dyspnea. However, doctors need to take a person’s individual characteristics into account when interpreting this blood test.

Sources:

Maisel A, Mueller C, Adams K Jr, et al. State of the Art: Using Natriuretic Peptide Levels in Clinical Practice. Eur J Heart Fail 2008; 10:824.

O'Connor CM, Starling RC, Hernandez AF, et al. Effect of Nesiritide in Patients With Acute Decompensated Heart Failure. N Engl J Med 2011; 365:32.

Schneider HG, Lam L, Lokuge A, et al. B-type Natriuretic Peptide Testing, Clinical Outcomes, and Health Services Use in Emergency Department Patients With Dyspnea: a Randomized Trial. Ann Intern Med 2009; 150:365.

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