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Brain Natriuretic Peptide (BNP): A Marker for Heart Failure.

Brain natriuretic peptide (BNP) that is also referred to as B-Type Natriuretic Peptide was first discovered in the brain. It is now also known to be present within the heart. The ventricles of the heart are found to release BNP under a situation where the heart muscle cells are being stretched excessively. This process initiates a rise in the plasma concentration of BNP and is often used as a good marker in the management and diagnosis of congestive heart failure.

Facts about BNP:
[1]. Synthesised by myocytes as proBNP (inactive molecule).
[2]. Cleaved to release the active BNP part of the hormone.
[3]. BNP is secreted by ventricular muscles when experiencing volume overload and myocardial wall stress.
[4]. By a process of enzymatic degradation the BNP and NT-proBNP are found to be cleared by the kidneys.
[5]. Half life of BNP is 23 minutes whereas for NT-proBNP it is 60-120 minutes.

       

Clinical significance:
Clinical researchers and hospital doctors have been aware of the important significance of measuring BNP levels for over 30 years. However, it has only in the last 10 or so years that a simple, quick and automated immunoassay has been developed that allows them to analyse BNP in a clinical laboratory to study potential heart condition related patients.

Even though the BNP test is easy to perform, in order for the test results to be reliable and accurate, subject patients must reframe from eating and drinking anything for up to 8-12 before proceeding with the test (only water is allowed). The blood sample which is to be used for the test needs to be collected from the veins.



The BNP levels present in the blood are measured in units of 'picograms per milliliter' (pg/mL). In normal patients the expected level of BNP is anything between 0-99pg/mL. However, anything above this amount is seen as being abnormal and is an indication of heart failure, higher levels have been found to range from 100 to 900pg/mL. The severity of heart failure increases with increasing amounts of BNP present. As a general rule of thumb the below BNP levels can be taken as a good indication of the degree of heart failure:

[1]. 100-300pg/mL : potential/acute.
[2]. > 300pg/mL : mild.
[3]. > 600pg/mL : moderate.
[4]. > 900pg/mL : critical.

Higher levels of BNP in the blood are known to indicate:
- abnormal functioning of heart.
- greater levels of fluid in the heart.
- greater pressure build up in the heart.
- greater probability of death (particular to patient with heart disease).

Medications are available which can be prescribed by your GP in order to help reduce the levels of BNP in the blood. Over a period of time the BNP test can be repeated to monitor the effectiveness of the treatment prescribed. If the medication is working then the patient should see a gradual reduction in the BNP reading over time until eventually the reading obtained is within the normal range (0-99pg/mL). This should also result in the patient showing a reduced or even none of the symptoms that are linked to heart failure.

One thing to bear in mind is that since there are many different kits available which can all potentially give different results due to their different cut-off points, it is necessary to use a kit which is suitable for the range you are looking to determine and also not to mix and match kits between different suppliers. This will ensure a level of accuracy and reproducibility is maintained. Also, if one is looking to compare results from different clinical trials then using assay kits which are different makes the results difficult to correlate and interpret.

Conclusion:
[a]. There have been many research papers over the last 10 years which have validated the usefulness of BNP tests in aiding the diagnosis and management of acute heart related failures.

[b]. This enzyme immunoassay kit has only been available recently and is a useful tool which allows physicians at busy accident and emergency departments to make quick and reliable evaluations on individuals with acute dyspnea. This can help reduce the cost of hospital stay and may even lead to a decrease in the time required to be discharged.

[c]. However, for this BNP test kit to be used appropriately and effectively physicians will need to understand its limitations as well as its benefits.


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