Why is BNP (B-type Natriuretic Peptide) High? Causes, Symptoms, and What to Do

A high B-type natriuretic peptide (BNP) means your heart muscle is under more stretch or strain than usual, and the most common reason is heart failure – the heart not pumping or filling as well as it should. BNP is also raised by other conditions, including atrial fibrillation, kidney disease, a blood clot in the lung (pulmonary embolism), lung conditions that strain the right side of the heart, severe infection, and simply older age. A high result is a reason for further heart tests, usually an echocardiogram, not a diagnosis by itself; a low BNP, on the other hand, makes heart failure unlikely.

What BNP and NT-proBNP are

When heart muscle is stretched – usually because the heart is working harder to pump or is holding too much blood – it releases a hormone called BNP. BNP widens blood vessels and helps the kidneys get rid of salt and water, which lowers the heart's workload. The heart actually makes a larger precursor molecule, proBNP, which splits into two parts in equal amounts: active BNP and an inactive fragment, NT-proBNP. Laboratories measure one or the other.

Usual thresholds

BNP and NT-proBNP are reported in pg/mL, which is the same number as ng/L. Everyone has some BNP; levels are interpreted for age, sex and the setting. Cut-offs used by European heart failure specialists:

Many laboratory reports simply flag BNP above 100 pg/mL as abnormal. Ranges and methods vary between laboratories, so compare your result with the range on your own report. BNP and NT-proBNP numbers are not interchangeable – an NT-proBNP of 300 is not the same as a BNP of 300.

Causes of a high BNP

Heart causes (most common)

• Heart failure – the main reason the test is done; higher levels generally go with more severe heart failure.
• Atrial fibrillation or flutter – an irregular heart rhythm raises BNP, sometimes above heart-failure thresholds even without heart failure.
• Heart valve disease and heart muscle disease, including a thickened heart muscle (left ventricular hypertrophy), whose most common cause is long-standing high blood pressure.
• Acute coronary syndrome (heart attack or unstable angina) – BNP rises, though it is not used to diagnose these.

Non-heart causes

• Kidney disease – reduced kidney function raises levels, partly through reduced clearance; doctors may use higher cut-offs when eGFR is below 60.
• Pulmonary embolism (a clot in the lung) and pulmonary hypertension (high pressure in the lung arteries), which strain the right side of the heart.
• Lung disease such as severe COPD or pneumonia, when it puts strain on the right heart.
• Severe infection (sepsis).
• Less often: anaemia, advanced liver cirrhosis with fluid in the abdomen, an overactive thyroid, and a recent stroke.
• Older age and female sex – both are linked with higher normal levels.

Medicines

• Sacubitril/valsartan, a heart failure medicine, blocks the enzyme that breaks down BNP, so BNP can rise while the heart is actually improving. NT-proBNP is not broken down this way, so it is the preferred test for people taking this medicine.

What a low BNP means

A BNP or NT-proBNP below the rule-out thresholds makes heart failure unlikely, and doctors then look for other causes of symptoms such as breathlessness. A low value is not harmful in itself. Two cautions: obesity lowers BNP and NT-proBNP (experts suggest cut-offs up to 50% lower in people with obesity), and heart failure with preserved ejection fraction (a stiff heart that pumps normally) tends to give lower levels. So a normal result may not rule out heart failure if it is still strongly suspected.

NT-proBNP vs BNP

• Both come from the same molecule and rise for the same reasons.
• BNP is active and lasts about 20 minutes in the blood; NT-proBNP is inactive and lasts about 60–120 minutes.
• NT-proBNP is more strongly affected by age and kidney function, which is why age-based cut-offs are used.
• NT-proBNP is not pushed up by sacubitril/valsartan, so it is preferred for monitoring people on that medicine.

Either test can be used; what matters is using the right cut-offs for the test and comparing repeat results from the same test.

Symptoms

BNP itself causes no symptoms. Symptoms come from the underlying condition – for heart failure these include shortness of breath (especially lying flat), swelling of the feet, legs or abdomen, tiredness, coughing, needing to pass urine at night, and loss of appetite.

What usually happens next

• Echocardiogram (heart ultrasound) is the key next test after a raised BNP.
• Heart rhythm check (ECG), since atrial fibrillation changes interpretation.
• Kidney function (creatinine/eGFR), since reduced kidney function raises levels and may call for higher cut-offs.
• Troponin if a heart attack is a concern.
• In people already known to have heart failure, the result is compared with their usual "stable" level: a change of at least 50% is usually needed before it is considered meaningful.

Frequently asked questions

What does a high B-type natriuretic peptide mean? It means your heart is under strain. Heart failure is the most common reason, but atrial fibrillation, kidney disease, a lung clot, lung disease, sepsis and older age can also raise it. Further tests, especially an echocardiogram, are needed to find the cause.

What is a normal BNP level? For most labs, BNP below 100 pg/mL is normal, and in people with mild, gradual symptoms a BNP below 35 pg/mL (NT-proBNP below 125 pg/mL) makes heart failure unlikely.

Is a low BNP good? Usually yes – it makes heart failure unlikely. In people with obesity, or with suspected heart failure with preserved ejection fraction, a low value may be falsely reassuring.

What is the difference between NT-proBNP and BNP? They come from the same precursor. NT-proBNP lasts longer in the blood, depends more on age and kidney function, and is not pushed up by sacubitril/valsartan. Their numbers cannot be compared directly.

Why is NT-proBNP important? It helps rule heart failure in or out, shows how severe it is and helps judge outlook. It is the preferred marker in people taking sacubitril/valsartan.

Does high BNP always mean heart failure? No. Heart failure is the most common cause, but several heart, lung and kidney conditions and older age raise BNP too.

When to see a doctor

If a routine test shows a raised BNP or NT-proBNP and you feel well, it is worth discussing with your doctor soon so the cause can be found, usually with an echocardiogram. Do not stop or change any heart medicine on your own.

Seek urgent care if you have chest pain, severe or sudden shortness of breath, breathlessness that stops you lying flat, or fainting.

Sources

1. Natriuretic Peptide Tests (BNP, NT-proBNP) — MedlinePlus, U.S. National Library of Medicine
2. Brain natriuretic peptide test — MedlinePlus, U.S. National Library of Medicine
3. Heart Failure Association of the ESC practical guidance on the use of natriuretic peptide concentrations — European Journal of Heart Failure (University of Glasgow repository)
4. Clinical Applications of Natriuretic Peptides in Heart Failure and Atrial Fibrillation — International Journal of Molecular Sciences (PMC)
5. B-type Natriuretic Peptide During Treatment with Sacubitril/Valsartan: the PARADIGM-HF Trial — Journal of the American College of Cardiology (PMC)
6. Heart Failure — Merck Manual Professional Version
7. KSHF Guidelines for the Management of Acute Heart Failure, Part I (Table 6, from the 2016 ESC heart failure guideline) — Korean Circulation Journal (PMC)
8. Left Ventricular Hypertrophy — Cleveland Clinic

Decisions about your health should always be made in consultation with your healthcare provider.