Natriuretic peptides are hormones released by the heart when its walls are stretched, and blood tests for them, BNP and NT-proBNP, are the main lab tests for heart failure. For someone without sudden symptoms, heart failure is unlikely if BNP is under 35 pg/mL or NT-proBNP is under 125 pg/mL. For sudden breathlessness, the rule-out cutoffs are under 100 and under 300 pg/mL.[1] US guidelines give these tests the strongest level of recommendation for diagnosing heart failure and judging outlook.[2]
This page is part of our peptide basics hub. Natriuretic peptides are a good example of how lab-made versions of natural peptides are developed; see natural vs synthetic peptides.
Bottom line
- Established: BNP and NT-proBNP help rule heart failure in or out, and higher levels predict a worse outlook.[1][2][3]
- Established: levels run lower in people with obesity, which can hide heart failure.[4][5]
- Mixed: using repeated tests to steer treatment did not help in the largest trial.[7]
- Promising: screening at-risk people with BNP reduced heart dysfunction in one trial.[6]
The three natriuretic peptides
| Peptide | Main source | Main role | Clinical use |
|---|---|---|---|
| ANP (atrial natriuretic peptide) | Upper heart chambers (atria) | Salt and water loss, vessel relaxation | Mostly research |
| BNP (B-type natriuretic peptide) | Lower heart chambers (ventricles) | Same, released with wall stretch | BNP and NT-proBNP blood tests |
| CNP (C-type natriuretic peptide) | Blood vessel lining, bone growth plates | Local vessel tone, bone growth | Basis of vosoritide |
BNP starts as a longer precursor called proBNP. It splits into active BNP and an inactive piece, NT-proBNP. NT-proBNP stays in the blood longer, so its values run higher, and labs report the two on different scales.
How the tests diagnose heart failure
The landmark study. The Breathing Not Properly study tested BNP in 1,586 people arriving at emergency departments with sudden shortness of breath. BNP was more accurate than any history, exam finding or other lab test at identifying heart failure. A cutoff of 100 pg/mL was 83.4% accurate, and a level below 50 pg/mL had a 96% negative predictive value, meaning heart failure was very unlikely.[3]
Current cutoffs. The 2021 European Society of Cardiology guideline uses these rule-out values:[1]
| Setting | BNP | NT-proBNP |
|---|---|---|
| Gradual symptoms (clinic) | Under 35 pg/mL | Under 125 pg/mL |
| Sudden symptoms (emergency) | Under 100 pg/mL | Under 300 pg/mL |
Results above these levels don’t confirm heart failure on their own. They mean an echocardiogram (heart ultrasound) is needed. The 2022 US guideline recommends these tests to support diagnosis when heart failure is suspected and to estimate prognosis.[2] A 2026 update to the universal definition of heart failure frames the condition around symptoms plus objective evidence of a heart abnormality, with biomarkers as one part of that evidence.[11]
Why obesity lowers levels
In 3,389 Framingham Study participants without heart failure, average BNP fell as body weight rose. Among men, adjusted BNP was 21.4 pg/mL in lean, 15.5 in overweight and 12.7 in obese participants, with similar results in women. Diabetes also lowered levels.[4]
A 2024 pooled analysis of 24,455 people from three trials found the same inverse link between body mass index and NT-proBNP. At any given NT-proBNP level, people with higher BMI had a higher risk of heart failure hospitalization.[5] In practice, a “normal” result in someone with obesity reassures less than it would in a lean person. That matters for readers using weight-loss drugs; heart benefits of those medicines are covered in our GLP-1 heart outcomes guide.
Using the tests for screening and treatment
Screening (STOP-HF, 2013). In 1,374 people with risk factors such as high blood pressure or diabetes, yearly BNP testing with referral for heart ultrasound when BNP reached 50 pg/mL or more lowered the rate of heart dysfunction or heart failure: 5.3% versus 8.7% with usual care. Emergency cardiovascular hospitalizations also fell.[6]
Guiding treatment (GUIDE-IT, 2017). In 894 high-risk people with reduced-pumping heart failure, adjusting treatment to lower NT-proBNP did not reduce hospitalization or cardiovascular death compared with usual care (37% in both groups). The trial was stopped early for futility.[7]
Rapid follow-up after discharge (STRONG-HF, 2022). In 1,078 people hospitalized for acute heart failure, an intensive plan that raised medicines to full doses within two weeks, with close monitoring that included NT-proBNP, was stopped early because the difference between groups was larger than expected.[8] The benefit came from the whole care strategy, not the test alone.
Natriuretic peptides as medicines
- Nesiritide is a lab-made version of human BNP. In ASCEND-HF, 7,141 people with acute heart failure received it or placebo. It did not significantly improve breathlessness by the trial’s preset standard, or reduce 30-day rehospitalization or death (9.4% vs 10.1%).[9]
- Vosoritide is a modified CNP. In a phase 3 trial of 121 children with achondroplasia, the most common form of dwarfism, daily injections increased growth rate over 52 weeks versus placebo.[10] It is FDA-approved for this use. See our list of FDA-approved peptides.
These are separate from the peptides often discussed online. Their approval came through large, controlled trials, which is the standard to compare other peptide claims against.
Limitations
- Cutoffs are averages. Age, kidney function, weight and heart rhythm all shift results.[1]
- BNP and NT-proBNP values aren’t interchangeable, and results can differ between lab assays.
- Some heart medicines, such as sacubitril/valsartan, raise BNP but not NT-proBNP, so clinicians usually track NT-proBNP in people taking them.
What’s next
Research is focused on age-adjusted cutoffs to reduce false alarms in older adults, on point-of-care testing in primary care, and on how obesity treatment changes these levels. Natriuretic peptides are one family of the body’s own signaling peptides; antimicrobial peptides are another, covered in LL-37 vs defensins vs magainin.
Questions to discuss with a clinician
- What was my BNP or NT-proBNP level, and how does my age, weight and kidney function affect what it means?
- Do I need an echocardiogram?
- Should my level be rechecked, and what change would matter?
- If I have risk factors like high blood pressure or diabetes, would screening help me?
