BNP is released into the blood circulation by cardiac cells whenever the pressures within the heart become abnormally elevated. 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 somebody experiences acute worsening of heart failure, her BNP levels typically become very high.pulmonary embolus). If BNP levels are very high, that's usually a sign that cardiac pressures are greatly elevated, and that heart failure is very likely to be the cause of dyspnea.
When Are BNP Levels Measured?Most typically, doctors will measure the BNP blood levels when a patient comes in with acute or worsening dyspnea, and the doctor is not quite sure of the cause. This situation is not that unusual, because many patients with chronic heart failure (especially smokers) also have chronic lung disease, and it can sometimes be quite difficult to tell which of these conditions is producing the dyspnea. Measuring BNP levels can be a quick and relatively easy way to help distinguish which underlying medical disorder is causing the acute problem.
When Are BNP Levels Considered High?While the "normal" level of BNP varies among individuals (levels are usually higher in older people than in younger people, and in women than in men, but lower in obese people than in non-obese people), normal levels in everyone are usually below 100 pg/ml.
So a BNP level below 100 pg/ml most often means that heart failure is NOT the cause of acute dyspnea.
A BNP level that's elevated above 400 pg/ml means that heart failure is very likely to be the cause of the patient's dyspnea.
And BNP levels between 100 and 400 pg/ml are simply not very helpful in determining whether heart failure is the cause of the patient's symptoms, which could be due to heart failure or something else. If BNP levels are between 100 and 400 pg/ml, other diagnostic testing, such as an echocardiogram, will be necessary.
Is BNP Helpful in Treating Heart Failure?The chief utility of BNP measurement is that it can be helpful in diagnosing whether or not heart failure is the cause of a patient's dyspnea.
Once heart failure has been diagnosed, some doctors believe that following repeated measurements of BNP can help guide their therapy (for instance, by helping them decide whether they have given enough diuretic medication). But clinical trials have failed to demonstrate that treatment guided by serial BNP measurements is useful in improving the outcome of therapy, so most doctors use BNP blood tests only if they need help with the diagnosis.
NesiritideSeveral years ago, there was a lot of excitement around the use of BNP itself as a treatment for heart failure. After all, BNP is a hormone that does many of the things doctors are usually trying to accomplish in treating heart failure (namely, reducing the body's salt and water content, and lowering blood pressure).
The drug nesiritide (Natrecor), which consists of a form of BNP, 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 (which has to be given intravenously) significantly improved the outcomes of patients with heart failure. In the past few years, its usage has fallen drastically, and its usage today is largely limited to patients who fail to respond adequately to more routine heart failure therapy.
SummaryThe next time your husband's doctor mentions BNP, you should now have enough information to ask the right questions. Why does he/she find BNP measurement useful in your husband's case? (Is there some question regarding the correct diagnosis?) How high are the BNP levels? Does he/she believe that repeated BNP measurements are helping to guide your husband's therapy? Is he/she considering nesiritide therapy?
By asking such questions, not only will you learn a little more about your husband's heart failure, but you will also demonstrate to the doctor that you are a person who understands something about heart failure, and perhaps a person who deserves a little more of his/her time.
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.