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Heart failure happens when the heart can’t pump blood well enough and fluid builds up in your lungs, legs and abdomen. It is usually the result of long-term damage or strain on the heart rather than a single sudden event. Heart failure is sometimes referred to as congestive heart failure (CHF).
Heart failure does not mean that the heart has stopped working — it means it is weaker, stiffer or less efficient than it should be. The heart muscle has become too weak to pump blood, or the heart becomes too stiff to fill up with blood properly, or both. When the heart cannot move blood forward efficiently, pressure builds up behind it. When this happens, blood backs up in the lungs or body fluids build up.
The heart tries to compensate in order to maintain blood pressure and flow. The heart beats faster and harder, blood vessels constrict and kidneys retain sodium (salt) and water (to increase blood volume and therefore blood pressure). This works in the short term but in the long terms it puts more stress on the heart and makes things worse.
What are BNP and NT-proBNP?
When the heart senses it is being stretched by an increased blood volume, heart muscle cells release hormones called natriuretic peptides (both BNP and NT-proBNP are types of natriuretic peptides).
These hormones send chemical messages to your kidneys to get rid of sodium and water. Removing sodium lessens the amount of water in your blood - less water means lower blood volume and as a result, lower blood pressure.
At the same time, natriuretic peptides help relax the blood vessel walls which also leads to lower blood pressure. For more on how blood pressure is managed by your kidneys see Sodium.
If you have high levels of natriuretic peptides in your blood, it can be a sign that your heart is under stress.
BNP and NT-proBNP are produced mainly in the heart’s left ventricle (the main pumping chamber).
How the heart pumps blood
1. The heart fills with blood
2. The heart squeezes
Heart failure
Symptoms of heart failure in the early stages can be non-specific or else similar to those of other health problems. If you have heart failure, you may be experiencing swelling in the legs (oedema), difficulty breathing, shortness of breath and tiredness or weakness. In the early stages, symptoms are only apparent during physical activity but as the heart’s condition worsens, symptoms can occur at lower levels of physical exercise and eventually, at rest.
Heart failure can be confused with other health disorders especially lung disease, other conditions of the heart or sepsis (the body’s emergency response to infection) making it difficult to diagnose. An accurate diagnosis as early as possible is important because heart failure can be successfully managed with treatment.
Measuring BNP or NT-proBNP can show if your symptoms are due to heart stress or something else. It can help your doctors decide if you need to have further specific investigations, such as an ultrasound of the heart (called an echocardiogram) where high-frequency sound waves are used to examine your heart.
Acute heart failure
BNP and NT-proBNP are also used in the emergency department to quickly diagnose or rule out acute heart failure in someone with symptoms such as shortness of breath, chest pain and confusion or collapse. Acute heart failure is when there is a worsening of heart failure symptoms, and these can start suddenly.
Systemic sclerosis
BNP and NT-proBNP are also used to help monitor systemic sclerosis (scleroderma): a chronic autoimmune disorder in which the immune system damages blood vessels and causes scarring. This can affect the heart muscle leading to heart failure. BNP or NT-proBNP can help detect early heart involvement, assess risk and monitor progression or treatment response.
What is the difference between BNP and NT-proBNP?
ProBNP is a hormone released into the blood when heart ventricles are stretched by high blood pressure or excess fluid. It is made as a larger molecule which is split into:
BNP and NT-proBNP are released into the blood in equal amounts. Either can be tested for, but generally, NT-proBNP is preferred because it is more stable in blood and it stays in blood circulation longer than BNP. This makes measurements more reliable.
Sample
Blood.
Any preparation
None.
BNP and NT-proBNP are regarded as rule-out tests. They cannot diagnose heart failure by themselves, but they can help rule it out. If the test result is negative, your doctors can be confident that heart failure is very unlikely to be the cause of your symptoms and consider other reasons.
You doctors may start with an electrocardiogram (ECG), where electrical leads are placed on your chest, arms and legs to record the electrical signals travelling through your heart, and a chest X ray.
Blood tests may be ordered at the same time:
Results of tests are interpreted alongside your symptoms and a clinical examination.
Reference intervals - comparing your results to the healthy population
Your results will be compared to reference intervals (sometimes called a normal range).
If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.
Reference intervals for BNP and NT-pro BNP are not harmonised – the reference intervals on your test report will depend on the laboratory that performs your tests. The following results are a guide only.
NT-proBNP
| Test result | Levels | What they may mean |
| High | Age less than 50 years - NT-proBNP level of more than 450 ng/L Age 50-70 years -NT-proBNP level of more than 900 ng/L Age more than 70 years - NT-proBNP level of more than1800 ng/L | Heart failure is likely. NT-proBNP levels may be raised by factors other than heart failure, including:
|
| Low | NT-proBNP level of less 300 ng/L | Heart failure unlikely. Your doctors will consider other possible causes of your symptoms. |
Reference intervals for NT-proBNP are not harmonised because levels increase with age, they are higher in women than men and are higher in someone who is slim and lower in someone carrying more fat. However, there is international agreement on the clinical decision cut-offs given above. Measured as nanograms per litre. | ||
BNP
| Test result | Levels | What they may mean |
| High | A BNP level of more than 500 ng/L | Congestive heart failure is likely. BNP levels may be raised by factors other than heart failure, including acute coronary syndrome (a sudden blockage of blood flow to the heart muscle), a blood clot in the lungs (pulmonary embolism), shock, abnormal heart rhythm (atrial arrhythmia), severe pneumonia and kidney (renal) disease. |
| Equivocal | A BNP level of 100-500 ng/L | This result is unclear and a diagnosis will need to be made on tests such as an echocardiogram. |
| Low | A BNP level of less than 100 ng/L | Heart failure unlikely. Your doctors will consider other possible causes of your symptoms. |
Reference intervals for BNP are not harmonised because levels increase with age, they are higher in women than men and are higher in someone who is slim and lower in someone carrying more fat. However, there is international agreement on the clinical decision cut-offs given above. Measured as nanograms per litre. | ||
You may see the terms EF and LVEF on your results form. The ejection fraction (EF) is a way to measure how well your heart is pumping blood. It measures how much blood your left ventricle (LV — a chamber in your heart) pumps out with every heartbeat. A healthy heart will have an LVEF of 55 to 70 percent.
People with heart failure can be diagnosed with:
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.
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