BNPvsNT-proBNP

BNP and NT-proBNP measure the same thing, how much the heart's walls are being stretched, using two different fragments of one molecule. The question they answer is the same; the numbers are not. A BNP of 300 pg/mL and an NT-proBNP of 300 pg/mL mean very different things.

What is the difference between BNP and NT-proBNP?

When the heart's chambers are stretched by high pressure or extra fluid, heart muscle cells release proBNP, which is cut into two parts. BNP (B-type natriuretic peptide) is the active hormone: it widens blood vessels and helps the kidneys shed salt and water. NT-proBNP (N-terminal proBNP) is the leftover fragment with no known job. Both are reasonable stand-ins for the filling pressures and volumes inside the heart, and both have very high accuracy for telling heart failure apart from other causes of breathlessness. ¹

The difference is how long each lasts. BNP is cleared within minutes, partly by an enzyme called neprilysin; NT-proBNP is cleared more slowly. Calculated half-lives are about 13 to 20 minutes for BNP and 25 to 70 minutes for NT-proBNP. ⁶ That is why NT-proBNP circulates at higher concentrations and why its cut-offs are higher. The BNP marker page and NT-proBNP marker page cover each in detail.

Absolute levels of BNP and NT-proBNP are not interchangeable and additionally depend on the assay used for measurement.Mair J. Comparison of B-type natriuretic peptide and N-terminal proBNP in daily clinical practice. European Cardiology, 2008 ⁶

BNP and NT-proBNP side by side

How the cut-offs work

Natriuretic peptide tests are best at ruling heart failure out. The 2021 European Society of Cardiology heart failure guideline treats heart failure as unlikely, outside an emergency, with a BNP under 35 pg/mL or an NT-proBNP under 125 pg/mL. For someone who arrives with sudden breathlessness, the rule-out levels are higher: BNP under 100 pg/mL or NT-proBNP under 300 pg/mL. ² Above those levels, an echocardiogram (heart ultrasound) is the usual next step, because the blood test shows strain but not its cause. ¹

The 2022 American heart failure guideline also recommends measuring BNP or NT-proBNP in people with breathlessness to support or exclude a diagnosis of heart failure, and for judging outlook. ³ Neither guideline prefers one test over the other for diagnosis; a 2019 European practical guide found BNP and NT-proBNP have comparable diagnostic and prognostic accuracy. ¹

NT-proBNP has age-based cut-offs in emergencies

NT-proBNP rises with age even without heart failure. In an international study of 1,256 breathless patients, the cut-offs that best confirmed acute heart failure were 450 pg/mL under age 50, 900 pg/mL from 50 to 75, and 1,800 pg/mL over 75. A single age-independent level of 300 pg/mL ruled acute heart failure out with a 98% negative predictive value. ⁴

What moves both results besides heart failure

• Age and female sex: both peptides run higher in older adults and in women. ⁶
• Kidney function: both rise as filtering falls, so a mild rise reads differently in chronic kidney disease. Check the eGFR alongside. ⁶
• Atrial fibrillation and other rhythm problems raise both. See heart rhythm.
• Heart valve disease, a recent heart attack, and a clot in the lungs raise both. ¹
• Obesity lowers both, enough that lower cut-offs, about 50% lower, are suggested in people with obesity. ¹
• Severe illness such as sepsis raises both, so in shock they cannot tell a heart cause from another cause. ¹

Because these factors push both peptides in the same direction, they rarely change which test you should have. They change how a borderline result is read.

When BNP and NT-proBNP disagree

Most people only ever have one of the two tests, so disagreement usually shows up as a confusing trend after a switch of test or lab, or in someone starting a particular heart failure medicine.

BNP rising on sacubitril/valsartan

Sacubitril blocks neprilysin, one of the enzymes that breaks BNP down, so BNP levels can climb even while the heart is doing better. In the PARADIGM-HF trial, BNP doubled in 18% of patients during the first 8 to 10 weeks of sacubitril/valsartan, while such rises in NT-proBNP were extremely rare. Both peptides still predicted outcomes during treatment, but NT-proBNP gave less confusion in the first weeks after starting. ⁵ If you take this medicine, a rising BNP is a question for your cardiology team, not a reason to change anything yourself.

A switch between tests or labs

A BNP of 150 pg/mL last year and an NT-proBNP of 600 pg/mL this year do not show that things got four times worse. The two tests run on different scales, and even the same test can differ between assay makers. ⁶ Trend one test, ideally at the same lab. More on this in why a trend beats a single reading.

Kidney disease or older age

Both peptides rise as kidney function falls and with age, and the European guidance asks clinicians to read results in that context rather than against a single number, and a 2008 review notes that decision limits need adjusting for kidney function. ^{1 6} For NT-proBNP in emergencies, the age bands above already build part of this in. ⁴

A low result in someone with obesity

Excess body fat lowers both peptides, so a value slightly under the usual rule-out level is less reassuring in someone with obesity. ¹ Symptoms and an echocardiogram carry more weight here.

Which one should you ask about?

• If you have never had either: whichever your clinician's lab runs. For diagnosis, the two perform comparably. ¹
• If you are being followed over time: stay with the same test, and ideally the same lab, so results can be compared.
• If you take sacubitril/valsartan: NT-proBNP is the easier test to read, especially in the first weeks. ⁵
• If you have chronic kidney disease, atrial fibrillation or obesity: either test works, but ask how those factors shift your cut-off. ¹

These peptides measure strain on the heart wall. Damage to heart muscle, as in a heart attack, is measured by troponin; see high-sensitivity troponin T and troponin I. Long-term high blood pressure is one of the common reasons the heart works under strain.

To read your own result: check which of the two tests it is, compare it with that test's cut-offs (35 or 100 pg/mL for BNP, 125 or 300 pg/mL for NT-proBNP), and remember that age, kidney function, rhythm, weight and some medicines move the number. A clinician confirms what a raised result means with a heart scan.

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