BNP in Heart Failure

Heart failure
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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 an acute episode of severe dyspnea (breathlessness) caused by heart failure - is almost invariably accompanied by markedly elevated cardiac pressures. 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).

If BNP levels are very high, that usually indicates that cardiac pressures are greatly elevated - which means that heart failure is very likely to be present.

When Are BNP Levels Measured?

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

This situation is fairly common. Many patients who have chronic heart failure also have chronic lung disease (especially if they are smokers), and it can sometimes be quite difficult to tell which of these conditions is producing the acute symptoms. Measuring BNP levels can be a quick way to figure out which underlying disorder is the culprit.

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 patient'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. The doctor will have to rely on other diagnostic testing, such as an echocardiogram, to clinch the diagnosis.

Is BNP Helpful 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.

Sources:

Cowie MR, Struthers AD, Wood DA, et al. Value of natriuretic peptides in assessment of patients with possible new heart failure in primary care. Lancet 1997; 350:1349.

Tjeerdsma G, de Boer RA, Boomsma F, et al. Rapid bedside measurement of brain natriuretic peptide in patients with chronic heart failure. Int J Cardiol 2002; 86:143.

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.

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