Diagnostic Utility
In addition to the values of total cholesterol, LDL and HDL, the blood test reports can report the plasma concentrations of other less known cardiovascular risk markers. Among these, BNP and pro-BNP stand out, particularly useful for assessing the risk of heart failure (heart failure) and in general of left ventricular dysfunctions (such as cardiac ventricular hypertrophy).
Normal values
- In healthy subjects, BNP is present in circulation in concentrations of about 5-20 pmoles / ml.
BNP High - Causes
- The values of BNP, in addition to increasing physiologically with aging, are significantly increased in patients with left ventricular hypertrophy and heart failure.
- BNP can also rise in edematous pathologies that lead to an increase in atrial and ventricular pressure - such as renal insufficiency, liver cirrhosis with ascites, etc. - and in the presence of unstable angina and pulmonary hypertension.
Clinical meaning
- The BNP has a high negative predictive value especially with regard to heart failure (low risk of false negatives). This means that if its values are normal it is possible to exclude the presence of ventricular dysfunctions with a high degree of probability.
Not as good is the positive predictive value; this means that - especially at levels just above the normal limit - the BNP is a fairly accurate indicator of the presence of pathology (discreet risk of false positives).
- The BNP values are also correlated to the severity of decompensation and prognosis; this means that the greater the value of BNP and the greater the severity of the disease and the lower hopes of survival of the patient
- Since BNP levels represent a predictor of death and cardiovascular events in patients without a prior diagnosis of heart disease, the exam is considered a possible means of screening for the presence of heart failure.
- In patients with heart failure, measurement of BNP levels is a potentially useful means of monitoring response to treatment
- To summarize: the dosage of BNP (cerebral natriuretic peptide) or NT-proBNP (amino-terminal fragment of BNP) can have a significant relevance in assisting the clinician not only in the diagnosis, but also in the monitoring and treatment of heart failure congestive
Biological Role
BNP stands for Brain Natriuretic Peptide (Cerebral Natriuretic Peptide) or more correctly for B-type natriuretic peptide ( Type B Natriuretic Peptide ). The term "Brain" brain is indeed out of place and refers to the initial discovery of this peptide in pig brain extracts.
In reality, in humans the BNP is secreted above all by the ventricles of the heart in response to an excessive lengthening of their cardiac muscle cells, a sign of an increase in the ventricular volume or in the pressure of the end diastole inside the same ventricle.
A little review of pathophysiology:
- BNP is secreted by the ventricles of the heart in response to excessive elongation of the muscle cells of the ventricles
- the muscle cells of the cardiac ventricles stretch too much when these chambers fill up too much with blood and this happens when they are unable to empty themselves adequately during systole; this typically happens in some circumstances:
- there is a reduced contractility of the myocardium measured as an ejection fraction; in a nutshell when the heart muscle is unable to contract sufficiently and empty itself accordingly, for example because its more or less extensive area has died of a heart attack, or because cardiac muscle efficiency is reduced by the degeneration associated with aging, from severe ischemic heart disease or heart disease. This condition is typical of heart failure and congestive heart failure.
- the ventricle cannot empty itself sufficiently when there is a high resistance at the level of the arterial vessels, for example due to the presence of strictures (narrowing) and stiffening of the arterial walls given by the presence of atherosclerotic plaques (to better understand, imagine a hose to water) in which water flows, if we crush the pipe we note that downstream of the obstruction the pipe begins to swell more and more until it bursts).
- there are heart valve dysfunctions
In addition to being a useful marker for analyzing a patient's cardiovascular risk through blood analysis, BNP plays a very precise biological role in the human body.
Once again this role can be understood: if its concentrations increase in the presence of hypertensive frameworks, the secretion of the latter will have the aim of bringing back the arterial pressure into the norm as much as possible, lowering it. In fact, BNP binds and activates the receptors of atrial natriuretic factor (ANP).
BNP and ANP present significant similarities with regard to structure, biosynthesis and biological effects, underlined by their diuretic, natriuretic and vasodilatory activity (they increase the excretion of sodium and water through the kidney and dilate the lumen of the vessels).
BNP and ANP reduce blood volume and cardiac post-load, resulting in an increase in cardiac output, partly due to a higher ejection fraction. Not surprisingly, the clinical use of recombinant synthetic BNP (nesiritide) was proposed for intravenous use, to be used for short periods to reduce the symptoms of heart failure.
NT-pro-BNP
The BNP, a peptide of 32 amino acids, is not directly secreted as such but complexed to an N-terminal fragment of 76 aminoacids (forming a complex biologically inactive molecule known as NT-proBNP or more simply NT-BNP ; compared to BNP; NT -BNP is more stable and present in greater concentrations in the circulation).
