B-Type Natriuretic Peptide (BNP) and NT-proBNP

B-type natriuretic peptide is a hormone secreted by cardiomyocytes in response to ventricular wall stress, and together with its co-secreted N-terminal fragment NT-proBNP it is the principal biochemical marker of cardiac strain. Unlike the necrosis markers, these peptides report haemodynamic load rather than cell death.

Definition

B-type natriuretic peptide (BNP) is a cardiac hormone released as the prohormone proBNP is cleaved into biologically active BNP and the inactive N-terminal fragment NT-proBNP; both are secreted in response to ventricular stretch and are measured by immunoassay as markers of cardiac wall stress.

Scope

This topic covers the synthesis and processing of proBNP into active BNP and the inactive NT-proBNP fragment, the physiological actions of the natriuretic peptide system, and the biochemical and analytical factors that influence their measurement. It treats the natriuretic peptides as analytes of clinical biochemistry; clinical decision thresholds are cited as evidence rather than presented as instructions. A separate endocrinology node covers the natriuretic peptide hormone family more broadly.

Core questions

• What physiological stimulus triggers BNP and NT-proBNP secretion?
• How do BNP and NT-proBNP differ as analytes in stability and clearance?
• What are the physiological actions of the natriuretic peptide system?
• How do age, sex, renal function, and body mass affect peptide concentrations?
• Why is a wall-stress marker complementary to necrosis markers such as troponin?

Key concepts

• proBNP processing into BNP and NT-proBNP
• Ventricular wall stress as the secretory stimulus
• Natriuretic peptide system (natriuresis, vasodilation, RAAS opposition)
• Differential clearance and half-life of BNP versus NT-proBNP
• Influence of renal function and body mass on concentrations
• Wall-stress marker versus necrosis marker
• Neprilysin and peptide degradation

Mechanisms

When cardiomyocytes are subjected to increased wall stress from pressure or volume overload, they synthesise the prohormone proBNP, which is cleaved into biologically active BNP and the inactive N-terminal fragment NT-proBNP, both released into the circulation in roughly equimolar amounts. Active BNP acts through natriuretic peptide receptors to promote natriuresis and vasodilation and to oppose the renin-angiotensin-aldosterone system, counterbalancing fluid and pressure overload. BNP is cleared relatively rapidly via natriuretic peptide receptor C and the enzyme neprilysin, whereas NT-proBNP is cleared more slowly and largely renally, giving the two analytes different half-lives and reference ranges. Because the stimulus is mechanical strain rather than cell injury, these peptides index haemodynamic load and complement the necrosis markers.

Clinical relevance

BNP and NT-proBNP are the biomarkers most closely tied to cardiac wall stress, and understanding what raises and lowers them is part of interpreting cardiac biochemistry critically. This entry describes their physiology and analytics as evidence; it does not provide diagnostic cut-offs or treatment guidance for individual patients, and notes only that interpretation must account for age, renal function, and body mass.

Epidemiology

Natriuretic peptides are among the most widely used cardiac biomarkers after troponin, and their concentrations vary systematically with age, sex, renal function, and body mass index, which is why population characteristics are central to interpreting them.

Evidence & guidelines

Cohort evidence on natriuretic peptide measurement in the acute setting (Maisel et al., 2002), reviews of natriuretic peptide physiology (Levin, Gardner & Samson, 1998) and of biomarkers in heart failure (Braunwald, 2008), and European Society of Cardiology heart-failure guidance (McDonagh et al., 2021) describe how these peptides are positioned among cardiac biomarkers.

History

B-type natriuretic peptide was first isolated from porcine brain, which gave it the historical name 'brain natriuretic peptide', though it is produced predominantly by the ventricular myocardium. Its identification extended the natriuretic peptide family first defined by atrial natriuretic peptide, and the development of immunoassays for BNP and later NT-proBNP established them as routine cardiac analytes through the late 1990s and 2000s.

Debates

BNP or NT-proBNP — which analyte to measure?

The two peptides differ in stability, half-life, and dependence on renal clearance, and neprilysin-inhibitor therapy raises measured BNP while NT-proBNP is unaffected, so the choice between them is an analytical and interpretive judgement rather than a settled equivalence.

Key figures

• Alan S. Maisel
• Eugene Braunwald
• David G. Gardner

Seminal works

• maisel-2002
• epstein-1998
• braunwald-2008

Frequently asked questions

What is the difference between BNP and NT-proBNP?

Both come from the same precursor proBNP: BNP is the biologically active hormone and NT-proBNP is the inactive N-terminal fragment released alongside it. They are measured by different assays, have different half-lives and clearance routes, and so carry different reference ranges, even though both rise with cardiac wall stress.

Why does BNP reflect strain rather than heart-muscle damage?

BNP is actively synthesised and secreted by heart-muscle cells when the ventricle is stretched by pressure or volume overload, so it reports the mechanical load on the heart; this differs from troponin, which leaks out only when heart-muscle cells are injured.