What is the function of B-type natriuretic peptide (BNP)?

From the Guidelines

BNP (B-type natriuretic peptide) is a crucial hormone in regulating blood pressure, sodium levels, and fluid balance, and its levels are significantly elevated in heart failure, making it a valuable diagnostic and prognostic tool. The primary function of BNP is to promote diuresis, vasodilation, and inhibition of the renin-angiotensin-aldosterone system, which collectively reduce blood pressure and decrease cardiac workload 1.

BNP Function and Clinical Utility

BNP levels rise in response to stretching of heart muscle cells due to increased volume or pressure, and clinically, BNP testing is valuable for diagnosing heart failure, with levels typically above 100 ng/L suggesting heart failure and levels above 500 ng/L strongly indicating it, as seen in the European Heart Journal study 1. The test is particularly useful in emergency settings to differentiate between cardiac and non-cardiac causes of shortness of breath. BNP levels also help in monitoring treatment effectiveness and predicting prognosis in heart failure patients.

Interpretation of BNP Values

The interpretation of BNP values is crucial, and according to the European Heart Journal study, BNP levels can be interpreted as follows:

• HF unlikely: BNP levels < 100 ng/L
• Grey zone: BNP levels between 100-500 ng/L
• HF likely: BNP levels > 500 ng/L However, in patients with significant renal failure and body mass index > 35 kg/m2, different decision limits must be used 1.

Prognostic Value of BNP

BNP levels are also useful for risk stratification and predicting short- and long-term mortality, with an admission NT-proBNP concentration > 180 ng/L being strongly predictive of death by 76 days, and a value > 986 ng/L having the best balance of sensitivity and specificity for 1-year mortality 1. Changes in BNP levels during hospitalization are also useful for risk stratification and are independent predictors of death or hospital readmission.

Monitoring Treatment Effectiveness

The response to treatment can be monitored by a change in BNP levels, with the initiation of diuretic, angiotensin converting enzyme inhibitor (ACEI), or vasodilator therapy resulting in a measurable decrease in levels, and their withdrawal resulting in increases 1. NT-proBNP further allows the titration of therapy to achieve a maximal individual response by targeting specific levels.

Clinical Guidelines

Clinical guidelines, such as those from the National Institute for Health and Clinical Excellence, recommend the use of BNP testing in the diagnosis of heart failure, with normal serum natriuretic peptide levels defined as BNP levels < 100 ng/L or NT-proBNP levels < 400 ng/L, and raised serum natriuretic peptide levels defined as BNP levels between 100 ng/L and 400 ng/L or NT-proBNP levels between 400 ng/L and 2000 ng/L 1.

Key Points

• BNP is a valuable diagnostic and prognostic tool in heart failure
• BNP levels are significantly elevated in heart failure
• BNP testing is useful in emergency settings to differentiate between cardiac and non-cardiac causes of shortness of breath
• BNP levels help in monitoring treatment effectiveness and predicting prognosis in heart failure patients
• Different decision limits must be used in patients with significant renal failure and body mass index > 35 kg/m2
• BNP levels are useful for risk stratification and predicting short- and long-term mortality
• Changes in BNP levels during hospitalization are useful for risk stratification and are independent predictors of death or hospital readmission.

From the Research

BNP Function

• Brain natriuretic peptide (BNP) is a member of the natriuretic peptide family, which includes ANP, CNP, DNP, and urodilatin 2.
• BNP is mainly secreted by the cardiac ventricles and is synthesized as pre-proBNP, which is then cleaved into proBNP and finally into BNP and NT-proBNP 2.
• The biological action of BNP is mediated by the NPR-A receptor, and it is eliminated from the systemic circulation by a neutral endopeptidase and by a clearance receptor (NPR-C) 2.

Physiological Effects of BNP

• BNP has vascular, renal, and cerebral activities, which contribute to its action against fluid expansion 2.
• BNP causes vasodilatation, diuretic and natriuretic effects, and inhibits the sympathetic nervous system and the renin-angiotensin-aldosterone axis 3.
• BNP preferentially acts on the venous system, resulting in preload reduction, in contrast to atrial natriuretic peptide, which acts preferentially on the arterial system to reduce afterload 4.

Clinical Utility of BNP

• BNP is a useful marker for the diagnosis of heart failure, and its levels are increased in patients with heart failure 5, 3.
• BNP-guided treatment does not improve morbidity and mortality in extensively treated patients with chronic heart failure, but responders to treatment have a significantly better outcome 6.
• Synthetic recombinant human BNP, such as nesiritide, is a new promising parenteral treatment in decompensated heart failure 3.