Brain Natriuretic Peptide (BNP)

Brain natriuretic peptide is a biologically active peptide of 32 amino acids, with vasodilator and natriuretic properties, which 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 brain natriuretic peptide and may represent cardiac status over longer periods.¹

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 of any cause. It is an independent predictor of high LV end-diastolic pressure. BNP levels decrease after effective treatment of heart failure.

• The most commonly used decision threshold for BNP is 100 pg/ml.²
• BNP levels of more than 100 pg/ml have a greater than 95% specificity and greater than 98% sensitivity when comparing patients without CHF to all patients with CHF.¹
• Even BNP levels of more than 80 pg/ml have greater than a 93% specificity and 98% sensitivity in the diagnosis of heart failure.
• BNP levels rise with age. Mean BNP levels are:²
  • 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.

• Cardiac
  • Heart failure
  • Diastolic dysfunction
  • Acute coronary syndromes
  • Hypertension with left ventricular hypertrophy
  • Valvular heart disease (aortic stenosis, mitral valve regurgitation)
  • Atrial fibrillation
• Non-cardiac
  • 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
  • Hyperthyroidism

Assay of brain natriuretic peptide is therefore 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 levels correlate closely with the NYHA Classification of Heart Failure as well as the Goldman Activity Classification of Heart Failure.
• Normal concentrations virtually exclude the diagnosis of heart failure, and very high levels effectively diagnose the condition; intermediate values require confirmation by echocardiography.
• Assay of NT-proBNP has potential as part of a diagnostic triage in patients presenting with symptoms suggestive of heart failure or in screening populations at high risk.¹
• 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.¹

In a pilot study, BNP levels correlated highly with clinical outcomes:¹

• 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.

• Some areas in the UK currently offer BNP testing for those patients who are symptomatic and a diagnosis of heart failure is likely.
• BNP testing has a particularly important role in areas where there is a waiting list for echocardiography.
• Patients should first have had an ECG, chest x-ray, full blood count, renal function and electrolytes, liver function tests and thyroid function tests.