Synonym: B-type natriuretic peptide
Brain natriuretic peptide (BNP) levels increase markedly in left ventricular dysfunction and the level in heart failure correlates with symptom severity. BNP can therefore be an important clinical marker for the diagnosis of heart failure in patients with unexplained dyspnoea. Other clinical applications, such as screening for asymptomatic ventricular dysfunction, establishing the prognosis or guiding the titration of drug therapy and prediction of future cardiovascular events, are under investigation but have not yet been sufficiently validated for widespread clinical use.
BNP is a biologically active peptide of 32 amino acids and has vasodilator and natriuretic properties. BNP is cleaved from the 108-amino acid pro-brain natriuretic peptide released from the cardiac ventricles in response to stretching of the chamber. The second remnant after cleavage, N-terminal pro-brain natriuretic peptide (NT-proBNP), is a 76-amino acid peptide with no known biological function which circulates at higher concentrations than BNP and may represent cardiac status over longer periods.
The release of BNP appears to be in direct proportion to ventricular volume expansion and pressure overload. BNP increases with right or left systolic or diastolic heart failure. It is an independent predictor of high left ventricular end-diastolic pressure. BNP levels decrease after effective treatment of heart failure.
Although testing for BNP provides a useful adjunct to routine assessment for differentiating acute heart failure from other causes of breathlessness, other factors such as comorbid illnesses, age, chronic kidney disease and body mass may affect BNP levels in ways that can obscure the diagnosis of heart failure, particularly when this marker is used in isolation. Therefore, it is essential that BNP be used to aid diagnosis in addition to the patient's history, clinical signs and other investigations. The role of BNP in heart failure and whether it is a target to treat or risk identifier remain contentious.
There is currently no definite evidence of a clinical advantage between using either BNP assay or NT-proBNP assay.
- The most commonly used decision threshold for BNP is 100 pg/ml.
- BNP levels of more than 100 pg/ml have a greater than 95% specificity and greater than 98% sensitivity when comparing patients without congestive heart failure (CHF) to all patients with CHF.[2, 5]
- Even BNP levels of more than 80 pg/ml have a greater than 93% specificity and 98% sensitivity in the diagnosis of heart failure.
- BNP levels rise with age. Mean BNP levels are:
- 26.2 pg/ml in those aged 55-64 years.
- 31.0 pg/ml in those aged 65-74 years.
- 63.7 pg/ml in those aged 75 years and older.
- Women without CHF tend to have higher BNP levels than males of the same age.
Patients should have had an ECG, CXR, FBC, renal function and electrolytes tests, LFTs, lipid profile, TFTs and any other investigation relevant to the clinical presentation.
Potential causes of elevated brain natriuretic peptide levels
- Heart failure.
- Diastolic dysfunction.
- Acute coronary syndromes.
- Hypertension with left ventricular hypertrophy.
- Valvular heart disease (aortic stenosis, mitral valve regurgitation).
- Atrial fibrillation.
- Acute pulmonary embolism.
- Pulmonary hypertension (primary or secondary).
- Sepsis (possibly due to tissue hypoxia or secondary myocardial depression).
- Chronic obstructive pulmonary disease with cor pulmonale or respiratory failure.
- Acute or chronic kidney injury.
BNP levels may be lower than expected when heart failure is secondary to causes proximal to the left ventricle - eg, acute mitral regurgitation, mitral stenosis or atrial myxoma.
Potential use of brain natriuretic peptide measurement
Assay of BNP is a potential aid in the diagnosis of heart failure. BNP testing allows a rapid assessment for defining those patients warranting an echocardiogram and also has the potential to enable rapid changes in therapy for those already receiving treatment for heart failure.
- BNP testing is effective in screening for left ventricular systolic dysfunction and reduces the number of patients requiring an echocardiogram.[6, 7]
- BNP levels correlate closely with the New York Heart Association (NYHA) Classification of Heart Failure as well as the Goldman Specific Activity Scale of Heart Failure.
- Normal concentrations virtually exclude the diagnosis of heart failure, and very high levels effectively diagnose the condition; intermediate values require further evaluation.
- Assay of BNP has potential as part of a diagnostic triage in patients presenting with symptoms suggestive of heart failure or in screening populations at high risk.
- In several pilot studies, BNP levels had a strong correlation with the severity of illness and were very reliable in differentiating heart failure from pulmonary disease.
- A pilot study has reviewed the role of finger prick testing for BNP at home and its usefulness in detecting decompensation. They found that BNP changes did help determine the risk of decompensation and it should complement other clinical markers of decompensation.
In a pilot study, BNP levels correlated highly with clinical outcomes:
- Patients with decreased BNP levels during their hospital stay, along with decreases in NYHA classification, had good outcomes.
- Patients whose hospital stay ended in death or readmission within 30 days of discharge had only minimal decreases of BNP levels or rising levels of BNP despite improvement or no change in their NYHA classification.
- The last measured BNP level was the single most reliable variable in predicting short-term outcomes in patients with heart failure.
Other potential clinical applications
- Raised plasma natriuretic peptide levels have been shown to predict the risk of death and cardiovascular events in people without heart failure after adjustment for traditional risk factors. Excess risk was apparent at natriuretic peptide levels well below current thresholds used to diagnose heart failure.
- Natriuretic peptides may help in identifying people at risk of stroke and atrial fibrillation.
- Admission BNP is an independent and powerful marker of early and late cardiac mortality in patients with acute chest pain without ST-segment elevation.
- Role in predicting stroke mortality.
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- Chronic heart failure: Management of chronic heart failure in adults in primary and secondary care; NICE Clinical Guideline (August 2010)
- Heart failure - chronic; NICE CKS, November 2010 (UK access only)
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