BNP and NT-proBNP
A blood sample drawn from a vein
B-type natriuretic peptide (BNP) and N-terminal pro b-type natriuretic peptide (NTproBNP) are peptide (small proteins) that are either hormones or part of the peptide that contained the hormone at one time. They are continually produced in small quantities in the heart and released in larger quantities when the heart senses that it needs to work harder. This supports fluid retention and volume expansion in the arteries and veins. Subsequently, the heart muscle is stretched and works hard to pump blood under normal resting condition. Tests for BNP and NT-proBNP measure their levels in the blood in order to detect and evaluate heart failure. The two tests are not interchangeable and should not be used together. Your healthcare practitioner should order one or the other but not both.
It is important to note that heart failure is an incorrect term. The heart still pumps blood, it just has difficulty doing so. If your healthcare practitioners treat you for heart failure, they have several approaches depending upon the severity of the disease.
BNP was initially called brain natriuretic peptide because it was first found in brain tissue (and to distinguish it from a similar protein made in the atria, or upper chambers, of the heart, termed ANP). BNP is actually produced primarily by cells in the left ventricle of the heart. The left ventricle is the heart's main pumping chamber and is responsible for sending oxygenated blood from the lungs to the remainder of the body. It is associated with blood volume and pressure and with the work that the heart must do in pumping blood throughout the body. Small amounts of a precursor protein, pro-BNP, are continuously produced by the heart. Pro-BNP is then split by the enzyme called corin to release the active hormone BNP and an inactive fragment, NT-proBNP, into the blood.
When the left ventricle of the heart is having difficulty pumping sufficient amounts of blood to the body, the concentrations of BNP and NTproBNP produced can increase markedly. This may occur with many diseases that affect the heart and circulatory system. The increase in circulating BNP or NT-proBNP will reflect this diminished capacity to deliver oxygenated blood to the body.
How is the test used?
A test for BNP or NT-proBNP is primarily used to help detect, support diagnosis, and in some instances evaluate the severity of heart failure. The two tests are not interchangeable and should not be used together. Your healthcare practitioner should order one or the other but not both.
A BNP test or NT-proBNP test can be used, along with other cardiac biomarker tests, to detect heart stress and damage and/or along with lung function tests to distinguish between causes of shortness of breath. Chest X-rays and an ultrasound test called echocardiography may also be performed. Your healthcare practitioner may also prescribe a stress test, which takes place on a treadmill.
Heart failure can be confused with other conditions, and it may co-exist with them. BNP and NT-proBNP levels can help healthcare practitioners differentiate between heart failure and other problems, such as lung disease. An accurate diagnosis is important because the treatments are often different and must be started as soon as possible.
Although BNP and NT-proBNP are usually used to recognize heart failure, an increased level in people who have had a heart attack may indicate an increased risk of further heart disease. Thus, a healthcare practitioner may use either BNP or NT-proBNP to evaluate risk of further heart disease in someone who has had a heart attack.
When is it ordered?
- Difficulty breathing, shortness of breath
- Swelling in the feet, ankles, legs, abdomen
Testing may be done in the emergency room or in a hospital bed when you are in crisis and/or have symptoms that could be due to heart failure and healthcare practitioners need to quickly distinguish whether you are suffering from heart failure or some other medical problem.
Several BNP or NT-proBNP tests may be done over a period of time when you are being treated for heart failure to monitor the effects of therapy.
What does the test result mean?
Higher-than-normal results suggest that you have some degree of heart failure, and the level of BNP or NT-proBNP in the blood may be related to its severity. Higher levels of BNP or NT-proBNP are often associated with an increased need for aggressive therapy. In some individuals with chronic heart failure, the markers may remain elevated and cannot be used to monitor response.
Normal results indicate that signs and symptoms are likely due to something other than heart failure.
Is there anything else I should know?
Levels of both BNP and NT-proBNP tend to increase with age in the absence of disease.
Levels of NT-proBNP and BNP may be increased in persons with kidney disease due to reduced clearance. Obese individuals may have lower concentrations of BNP or NT-proBNP.
While both BNP and NT-proBNP will rise with left ventricle dysfunction and either can be measured for diagnosis or monitoring therapy, they are not interchangeable and the results cannot be directly compared.
How common is heart failure?
According to the American Heart Association, more than 6 million people in the United States are living with heart failure and the number is growing. It is estimated that one in five American adults age 40 and older will develop heart failure in their lifetime. You may be at increased risk of developing heart failure if you have conditions such as heart disease, high blood pressure, or diabetes, or if you have had a heart attack. Other risk factors include tobacco use, alcohol use, and obesity.
How is heart failure treated?