B-Type Natriuretic Peptide (BNP) Test

Medically Reviewed by Zilpah Sheikh, MD on December 17, 2023
7 min read

BNP is a peptide (a short chain of amino acids) your heart and blood vessels make. It works as a hormone. That means it sends messages through your blood to other cells or organs in your body. Your heart makes BNP normally. Your heart will make more of it when it's working harder than it should to pump and move blood through your body.

When your blood vessels get the signal from BNP, it tells them to open up more to lower blood pressure and make it easier for your heart to pump your blood. The hormone also tells your kidneys to filter out more water and salt and get rid of it in your pee. Getting rid of water and salt is one way your body lowers blood pressure to make things easier on your heart.

BNP and a closely related peptide (called NT-proBNP for short) go by a few different names. These include:

  • B-type natriuretic peptide
  • Brain natriuretic peptide
  • NT-pro b-type natriuretic peptide
  • N-terminal pro-B-type natriuretic peptide

It might seem strange that a peptide your heart makes is sometimes called “brain natriuretic peptide.” But the reason is that scientists first found it in the brain. They later learned about its role in the heart and blood vessels. The word “natriuretic” is used to describe any substance that keeps your body from holding onto salt. It refers to the role of these peptides in telling your kidneys to get rid of more salt and water.

NT-proBNP is slightly different than BNP but closely related. It's an ingredient your body needs to make BNP. When your heart has to work harder, both BNP and NT-proBNP levels will go up.

When you have heart failure, your heart makes more B-type natriuretic peptide (BNP) and N-terminal-proBNP (NT-proBNP). Levels of both go up in your blood when your heart failure gets worse and go down when it gets better.

A BNP test measures your blood level of BNP. Sometimes, doctors might order a test that measures levels of NT-proBNP instead. Both tests tell you about the same thing. Doctors can use them to help diagnose or rule out heart failure when you have symptoms.

They're able to spot heart failure more than 80% of the time. If you already have heart failure, your doctor might also use one of these blood tests to see how your heart is doing and if your condition is getting better, worse, or staying the same. These tests can also help you find out if any treatments you're taking for heart failure are working or not.

BNP levels can help your doctor figure out if you have heart failure or something else that has similar symptoms, including shortness of breath. The test can also show if your heart failure has gotten worse. It’ll help your doctor decide what treatments you need and if you need to go to the hospital. It may also give them a look into what the future may hold for you. It's a sensitive test that allows your doctor to see if your heart failure is better or worse and whether or not your medicine is working well for you.

Depending on your medical center, your doctor may order tests for one or both peptides. They may order it when you have signs that might be heart failure or when you are being treated for heart failure. Signs of heart failure that may warrant a BNP test include:

  • Coughing that's dry or “hacking” and seems worse when you lie down
  • Trouble breathing
  • Shortness of breath or wheezing
  • Confusion
  • Feeling dizzy or fainting
  • Feeling fatigued or sluggish
  • Heart palpitations
  • Nausea, vomiting, or not wanting to eat
  • Swelling in your belly, legs, ankles, and/or feet
  • Peeing more than normal, especially at night

Having heart failure doesn't mean that your heart isn't working or has failed. It does mean your heart isn't pumping your blood as well as it should. But you should see your doctor or go to the emergency room right away if you think you may have heart failure or your heart failure is getting worse.

You don't need to do anything special to get ready to have a BNP test. A small amount of blood will be taken from you, using a small needle. It might sting or hurt a little bit when the needle goes into your arm or comes back out. But it shouldn't hurt a lot like any blood test. This part shouldn't take more than about 5 minutes.

Sometimes, you might get tested using a finger stick instead of drawing a vial full of blood. You're more likely to have this type if you're in the hospital as opposed to a clinic or doctor's office. It's possible to test your levels with just a few drops of blood.

They'll put your sample in a machine that measures how much BNP or NT-pro-BNP is in your blood. The test usually takes about 15 minutes to run. In some places, your blood sample may have to go to another lab for testing.

After they draw your blood, they'll put a bandage on your arm. You might notice a little soreness or a bruise later. But there aren't any serious risks from having a BNP blood test.

Your level of BNP can indicate if you have heart failure. The worse your condition gets, the higher your BNP levels rise. Testing BNP levels also is one of the best ways to show how well you're doing on heart failure treatment.

A normal BNP level is under 100 picograms per milliliter (pg/mL). A picogram is one-trillionth of a gram. A normal level of NT-proBNP is 125 pg/mL if you're under 75. If you are older than 75, a level under 450 pg/mL is normal.

Your levels and their meaning also will depend on other factors, including your:

  • Age
  • Sex
  • Other health conditions
  • Family history
  • Your weight
  • Medicines
  • Other test results

Normal BNP level

If your levels are in a normal range, it means you probably don't have heart failure. If you have symptoms, you might require other tests to find out the underlying cause.

High BNP level

If your levels are high, it may mean you have heart failure or that your heart failure is getting worse. But some other conditions can also make BNP go up.

Low BNP level

If your BNP levels are lower than they should be, there may be different reasons. Sometimes, this can happen even if you have heart failure, especially if you are obese. It's possible you could have a deficiency of BNP, which could make your body less able to handle changes in blood pressure or volume.

Other conditions that can cause your BNP levels to go up include:

  • Kidney failure
  • Other heart conditions
  • Some lung conditions, such as a blood clot (pulmonary embolism) or high blood pressure (pulmonary hypertension)

Ask your doctor to explain the results of your BNP tests and what they mean for your treatment and outlook.

Follow your doctor's advice, but you can take some steps at home in addition to treatment to help with your heart failure and get your BNP levels down. For instance:

  • One study found that people who cut down on the amount of salt in their diet lowered their BNP.
  • Another found that omega-3 fatty acids could lower BNP, but not a lot.
  • Eating a healthy diet with plenty of fruits and vegetables may help.
  • Avoid alcohol, which can weaken your heart muscle.
  • Avoid highly processed grains, such as white bread or pasta, and processed or cured meats.
  • Exercise therapy also can lower BNP levels significantly.

Doctors use BNP tests to see if your heart is working harder than it should, which happens when you have heart failure. BNP is a hormone your body makes naturally, but its levels go up when you have heart failure. BNP tests can help to see if your heart condition is getting better or worse or how well your heart failure medicine is working.

  • What does a high BNP mean?

A high BNP level means you may have heart failure or that your heart failure is getting worse. It may also mean your heart failure treatment isn't working well for you. Some other health conditions can cause BNP levels to go up, too. If you have high BNP and aren't sure what it means for your health or how to try and lower it, ask your doctor.

  • What does a BNP of 4,000 mean?

Your BNP levels tell you how hard your heart is working. A level of 500 to 1,000 pg/mL is considered mildly high or elevated. Levels of 2,000 to 3,000 are moderately high. When your BNP is 4,000 or higher, it means your levels are extremely high. One study found that there wasn't a lot of difference between people with moderate or higher BNP levels. If your BNP levels are very high, it may have more to do with your kidneys than your heart. You may have kidney dysfunction or failure in addition to heart failure. If your BNP levels are extremely high and you aren't sure what it means, talk to your doctor.