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Natriuretic Peptide

The B-type Natriuretic Peptide Test

The B-type Natriuretic Peptide (BNP) Test is a blood test for heart failure. It measures the level of B-type natriuretic peptide in your blood. Your heart's ventricles produce extra B-type natriuretic peptide when they can't pump enough blood to meet your body's needs. So if your B-type natriuretic peptide level is high, you probably have heart failure. The higher the levels are at diagnosis, the worse your heart failure is likely to be. The finding of low levels tends to exclude heart failure.

A variation of B-type natriuretic peptide called NT-proBNP (N-terminal prohormone B-type natriuretic peptide) has also been approved as a test for diagnosing congestive heart failure. When a molecule of B-type natriuretic peptide is released into the bloodstream by heart muscle cells, a molecule of NT-proBNP is also released. Both BNP and NT-proBNP tests may be useful in evaluating the risk of heart attack and other problems in patients who already have heart disease.

Doctors also use B-type natriuretic peptide levels to monitor the effectiveness of treatment. Once a heart failure patient has been on medication for a while and his heart function has improved and his heart size returned to normal or near-normal, his B-type natriuretic peptide level may drop because the heart produces B-type natriuretic peptide in response to abnormal pressures and heart enlargement. Other treated heart patients will show higher-than-normal levels even with a return to normal heart size and pressures.

Why is it important to avoid fluid overload?

In heart failure, the heart weakens and becomes unable to keep blood moving adequately through the heart and blood vessels. As a consequence, the flow of blood to the body's tissues decreases. Because the tissues don't receive the level of oxygen and nutrients they require, their efficiency and endurance decline. Poor circulation causes the kidneys not to be able to remove enough water, salt and waste products from the blood. In addition, decreased blood flow causes the kidneys to retain even more salt and water in an effort to increase blood volume.

In its attempt to satisfy the body's hunger for oxygen-rich blood, the heart may enlarge and beat faster. An increased blood volume causes blood vessels to distend with fluid and places an additional burden on the already overworked heart.

The normal balance of pressure between fluids inside and outside the blood vessels shifts. As a result, fluid that normally stays in the bloodstream leaks into surrounding tissue, causing fluid overload in the lungs, abdomen and/or legs, which often accompanies heart failure.

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