Brain natriuretic peptide
Encyclopedia
Brain natriuretic peptide (BNP), now known as B-type natriuretic peptide (also BNP) or GC-B, is a 32 amino acid polypeptide secreted by the ventricles
of the heart
in response to excessive stretching of heart muscle cells (cardiomyocytes). BNP is named as such because it was originally identified in extracts of porcine
brain, although in humans it is produced mainly in the cardiac ventricles.
BNP is co-secreted along with a 76 amino acid N-terminal fragment (NT-proBNP) which is biologically inactive. BNP binds to and activates the atrial natriuretic factor receptors NPRA, and to a lesser extent NPRB, in a fashion similar to atrial natriuretic peptide
(ANP) but with 10-fold lower affinity. The biological half-life
of BNP, however, is twice as long as that of ANP
, and that of NT-proBNP is even longer, making these peptides better targets than ANP for diagnostic blood testing.
The physiologic actions of BNP are similar to ANP and include decrease in systemic
vascular resistance
and central venous pressure as well as an increase in natriuresis
. Thus, the net effect of BNP and ANP is a decrease in blood volume which lowers systemic blood pressure and afterload, yielding an increase in cardiac output, partly due to a higher ejection fraction.
BNP > 100 pg per milliliter
BNP > 50 pg per milliliter
The effect or race and gender on value of BNP and its utility in that context has been studied extensively.
BNP can be elevated in renal failure BNP is cleared by binding to natriuretic peptide receptors (NPRs) and neutral endopeptidase (NEP) Less than 5% of BNP is cleared renally. NTproBNP is the inactive molecule resulting from cleavage of the prohormone Pro-BNP and is SOLELY reliant on the kidney for excretion. The achilles heel of the NT proBNP molecule is the overlap in kidney disease in the heart failure patient population.
!colspan=5| Usual ranges for brain natriuretic peptide
(BNP)
|-
!colspan=2| Patient type !! Lower limit !! Upper limit !! Unit
|-
|rowspan=4| Male > 45-54 yrs
4
40
pg/mL
|-
| 55-64 yrs
5
| 65-74 yrs 7
| 75-83 yrs 9
|rowspan=4| Female 45-54 yrs
8
| 55-64 yrs 10
| 65-74 yrs 13
| 75-83 yrs 16
155
The BNP test is used as an aid in the diagnosis and assessment of severity of congestive heart failure (also referred to as heart failure). A recent meta-analysis concerning effects of BNP testing on clinical outcomes of patients presenting to the emergency department with acute dyspnea revealed that BNP testing led to a decrease in admission rates and decrease in mean length of stay, although neither were statistically significant. Effects on all cause hospital mortality was inconclusive. The BNP test is also used for the risk stratification of patients with acute coronary syndromes.
When interpreting an elevated BNP level, it is useful to remember that values may be elevated due to factors other than heart failure. Lower levels are often seen in obese patients. Higher levels are seen in those with renal disease, in the absence of heart failure.
BNP is also one of the reasons why people will feel the need to urinate after getting into the bathtub or pool. The increased pressure on the body drives more fluid back into systemic circulation which in turn leads to a slight increase in preload. The left ventricle, and to a small degree the left atrium, secrete BNP in response. The natriuretic effect of BNP leads to an increase in urine production.
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
of the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
in response to excessive stretching of heart muscle cells (cardiomyocytes). BNP is named as such because it was originally identified in extracts of porcine
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
brain, although in humans it is produced mainly in the cardiac ventricles.
BNP is co-secreted along with a 76 amino acid N-terminal fragment (NT-proBNP) which is biologically inactive. BNP binds to and activates the atrial natriuretic factor receptors NPRA, and to a lesser extent NPRB, in a fashion similar to atrial natriuretic peptide
Atrial natriuretic peptide
Atrial natriuretic peptide , atrial natriuretic factor , atrial natriuretic hormone , or atriopeptin, is a powerful vasodilator, and a protein hormone secreted by heart muscle cells. It is involved in the homeostatic control of body water, sodium, potassium and fat...
(ANP) but with 10-fold lower affinity. The biological half-life
Biological half-life
The biological half-life or elimination half-life of a substance is the time it takes for a substance to lose half of its pharmacologic, physiologic, or radiologic activity, as per the MeSH definition...
of BNP, however, is twice as long as that of ANP
Atrial natriuretic peptide
Atrial natriuretic peptide , atrial natriuretic factor , atrial natriuretic hormone , or atriopeptin, is a powerful vasodilator, and a protein hormone secreted by heart muscle cells. It is involved in the homeostatic control of body water, sodium, potassium and fat...
, and that of NT-proBNP is even longer, making these peptides better targets than ANP for diagnostic blood testing.
The physiologic actions of BNP are similar to ANP and include decrease in systemic
Systemic circulation
Systemic circulation is the part of the cardiovascular system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart. This physiologic theory of circulation was first described by William Harvey...
vascular resistance
Vascular resistance
Vascular resistance is a term used to define the resistance to flow that must be overcome to push blood through the circulatory system. The resistance offered by the peripheral circulation is known as the systemic vascular resistance , while the resistance offered by the vasculature of the lungs...
and central venous pressure as well as an increase in natriuresis
Natriuresis
Natriuresis is the process of excretion of sodium in the urine via action of the kidneys. Natriuresis is promoted by Brain and Atrial natriuretic peptides, and it is inhibited by chemicals such as aldosterone...
. Thus, the net effect of BNP and ANP is a decrease in blood volume which lowers systemic blood pressure and afterload, yielding an increase in cardiac output, partly due to a higher ejection fraction.
Clinical significance
- The main clinical utility of either BNP or NT-BNP is that a normal level rules out heart failure.
- Either marker can also be used for screening and prognosis of heart failure.
- Both are also typically increased in patients with left ventricular dysfunction, with or without symptoms (BNP accurately reflects current ventricular status, as its half-life is 20 minutes, as opposed to 1-2 hours for NT-ProBNP).
BNP > 100 pg per milliliter
- sensitivity = 90%
- specificity = 76%
BNP > 50 pg per milliliter
- sensitivity = 97%
- specificity = 62%
- For patients with congestive heart failure, BNP values will generally be above 100 pg/ml.
- A more conservative interpretation of the BNP is that normal values are less than 50 pg/ml, in order to achieve adequate sensitivity.
- There is a diagnostic 'gray area', often defined as between 100 and 500 pg/ml, for which the test is considered inconclusive, but levels above 500 pg/ml are generally considered to be positive. This so called gray zone has been addressed in several studies and using clinical history or other available simple tools can help make the diagnosis.
- Bhalla et al. showed that BNP plays a very important role in prognostication of millions of diabetics.
- Also, BNP was found to have an important role in prognostication of heart surgery patients and in the emergency department. Bhalla et al. showed that combining BNP with other tools like ICG can improve early diagnosis of heart failure and advance prevention strategies. Utility of BNP has also been explored in various settings like preeclampsia , ICU and shock and ESRD.
The effect or race and gender on value of BNP and its utility in that context has been studied extensively.
| NYHA I | NYHA II | NYHA III | NYHA IV | |
|---|---|---|---|---|
| 5th Percentile | 33 | 103 | 126 | 148 |
| Mean | 1015 | 1666 | 3029 | 3465 |
| 95th Percentile | 3410 | 6567 | 10,449 | 12,188 |
BNP can be elevated in renal failure BNP is cleared by binding to natriuretic peptide receptors (NPRs) and neutral endopeptidase (NEP) Less than 5% of BNP is cleared renally. NTproBNP is the inactive molecule resulting from cleavage of the prohormone Pro-BNP and is SOLELY reliant on the kidney for excretion. The achilles heel of the NT proBNP molecule is the overlap in kidney disease in the heart failure patient population.
Brain natriuretic peptide
Brain natriuretic peptide , now known as B-type natriuretic peptide or GC-B, is a 32 amino acid polypeptide secreted by the ventricles of the heart in response to excessive stretching of heart muscle cells...
(BNP)
|-
!colspan=2| Patient type !! Lower limit !! Upper limit !! Unit
|-
|rowspan=4| Male >
|-
| 55-64 yrs
| 65-74 yrs
| 75-83 yrs
|rowspan=4| Female
| 55-64 yrs
| 65-74 yrs
| 75-83 yrs
The BNP test is used as an aid in the diagnosis and assessment of severity of congestive heart failure (also referred to as heart failure). A recent meta-analysis concerning effects of BNP testing on clinical outcomes of patients presenting to the emergency department with acute dyspnea revealed that BNP testing led to a decrease in admission rates and decrease in mean length of stay, although neither were statistically significant. Effects on all cause hospital mortality was inconclusive. The BNP test is also used for the risk stratification of patients with acute coronary syndromes.
When interpreting an elevated BNP level, it is useful to remember that values may be elevated due to factors other than heart failure. Lower levels are often seen in obese patients. Higher levels are seen in those with renal disease, in the absence of heart failure.
BNP is also one of the reasons why people will feel the need to urinate after getting into the bathtub or pool. The increased pressure on the body drives more fluid back into systemic circulation which in turn leads to a slight increase in preload. The left ventricle, and to a small degree the left atrium, secrete BNP in response. The natriuretic effect of BNP leads to an increase in urine production.
Measurement and standardisation
BNP and NT-proBNP are measured by immunoassay. BNP is standardised whereas NT-proBNP has not been standardised yet.See also
- N-terminal prohormone of brain natriuretic peptideN-terminal prohormone of brain natriuretic peptideThe N-terminal prohormone of brain natriuretic peptide is a 76 amino acid N-terminal fragment of brain natriuretic peptide.Both BNP and NT-proBNP levels in the blood are used for screening, diagnosis of acute congestive heart failure and may be useful to establish prognosis in heart failure, as...
(NT-proBNP) - Atrial natriuretic peptideAtrial natriuretic peptideAtrial natriuretic peptide , atrial natriuretic factor , atrial natriuretic hormone , or atriopeptin, is a powerful vasodilator, and a protein hormone secreted by heart muscle cells. It is involved in the homeostatic control of body water, sodium, potassium and fat...
- C-type natriuretic peptide