NT-proBNP test explained

NT-proBNP (N-terminal pro-B-type natriuretic peptide) is formed when the cells of the heart's ventricle produce the hormone BNP — its production increases when the heart wall is stretched by raised pressure or volume in the heart. As it is broken down, the BNP precursor releases two fragments: BNP itself and the inactive NT-proBNP, which stays in the blood longer and is therefore often considered the more convenient one to measure. The test is used above all when a person has symptoms resembling heart failure — breathlessness, swelling of the legs, abdomen or neck veins, tiredness — and the aim is to tell whether the cause lies in the heart or in another organ (for example the lungs or the kidneys). A low result usually allows heart failure to be ruled out, and the higher the result, the greater the likelihood that the symptoms are caused by the heart and the more severe the condition may be. NT-proBNP can also rise for other reasons — kidney failure, pulmonary embolism, pulmonary hypertension or a severe infection — so the result is always assessed by a doctor together with other tests and symptoms. When heart failure is suspected, NICE NG106 (recommendation 1.2.12) advises an ECG alongside NT-proBNP and considering further tests to look for aggravating factors or another cause of the symptoms: a chest X-ray, blood tests (kidney function, thyroid function, liver function, a lipid profile, glycated haemoglobin HbA1c and a full blood count), urinalysis and peak flow or spirometry.

• When breathlessness is felt, especially lying down or waking at night short of air
• When the legs, abdomen or neck veins swell
• When unusual tiredness or weakness is felt, or a cough appears
• When you often have to get up at night to pass urine, or your appetite disappears
• When heart failure is suspected and it needs to be told apart from symptoms caused by lung or kidney disease
• To monitor the course of already diagnosed heart failure, on a doctor's instruction

A raised NT-proBNP shows that the heart is working harder or is stretched, and it is most often linked with heart failure — the higher the result, the greater the likelihood and the more severe the condition may be. The result can also be raised by other causes that are not directly related to weakness of the heart muscle. MedlinePlus also lists heart valve disease and cardiomyopathy (disease of the heart muscle), and NICE NG106 names, among others, sepsis, liver cirrhosis, chronic obstructive pulmonary disease (COPD) and diabetes.

What can raise NT-proBNP

• Heart failure — the most common cause
• Kidney failure
• Pulmonary embolism
• Pulmonary hypertension
• Other lung problems

Symptoms that can occur alongside

• Breathlessness
• Swelling of the abdomen, legs, feet or neck veins
• Tiredness and weakness
• Cough
• Not being able to sleep lying flat
• Frequent urination at night
• Loss of appetite and nausea

What to discuss with a doctor

• Whether the symptoms (breathlessness, swelling) could have been caused by another reason — kidney or lung disease
• Further heart tests — an echocardiogram, an ECG — for a more precise assessment
• Kidney function markers, because they also affect the amount of NT-proBNP
• When it is worth repeating the test to follow how the condition changes over time

What a single result does not tell you

An NT-proBNP result on its own is not a diagnosis. A low result considerably reduces the likelihood that the symptoms are caused by heart failure, but the final assessment is always made by a doctor, taking into account symptoms, the examination and other tests. A raised result does not name its own cause either: besides heart failure, NT-proBNP can be raised by kidney failure, pulmonary embolism, pulmonary hypertension or a severe infection, so a doctor assesses it together with symptoms and other tests, for example an echocardiogram. The figures also cannot be compared directly with BNP figures, because the reference values of the two are different.