MK Community Cardio-Vascular Centre
25 Witham Court - Tweed Drive - Bletchley - MK3 7QU
Tel: 01908 272700 - Fax: 01908 630076

Brain Natriuretic Peptide Testing

Introduction:

Brain natriuretic peptide (BNP) now known as B-type natriuretic peptide also known BNP or GC-B is a protein secreted by ventricles of the heart in response to excessive stretching of the heart muscles.  BNP is named as such because it was originally identified in extracts of porcine brain although in humans it is produced mainly in cardiac (heart) ventricles.

Background

Heart failure is a complex syndrome that can result from any structural or functional cardiac disorder that impairs the ability of the heart to function as a pump and to support its physiological circulation (NICE guidelines).  The syndrome of heart failure is characterised by symptoms such as breathlessness, fatigue and signs such as fluid retention.  Diagnosing heart failure is not straightforward and requires a series of complex investigations along with clinical evaluation to arrive at that decision.

It is one of the most common conditions in industrialised society today- in the UK around 900,000 people have heart failure with a further similar number who have yet to develop symptoms (Peterson et al, British Heart Foundation 2002, cited in Full NICE guidelines).  The most common cause of heart failure in the UK is coronary heart disease with many patients having suffered a myocardial infarction in the past.  There is no single diagnostic test for heart failure and diagnosis is realised on clinical judgement based on a combination of history, full examination and appropriate investigations.

What is BNP and NT-proBNP?

There are two main types of BNP that are available for testing.  The first is brain-type natriuretic peptide i.e. BNP, which plays an important role in regulation of blood pressure, blood volume and sodium balance.  Once secreted the BNP precursor is split into biologically active peptide and the second type of BNP, the more stable amino-terminal prohormone fragment NT-proBNP, is secreted.

It is already known that N-terminal proB-type natriuretic peptide (NT-proBNP) levels provide sensitive and reasonably specific tests for diagnosis of heart failure and left ventricular dysfunction (Cowie et al, 1997: Talwar et al, 1999: Maisel et al, 2002: Moe 2005, cited in Heart Protection Study Group, 2007).  Furthermore, it is highly recommended also in NICE guidelines, and its results provide a good indicator of disease activity and prognosis of patients with heart failure.

Clinical Issues

Testing for NT-proBNP provides a useful adjuvant to routine assessment for differentiating heart failure from other aetiologies of dyspnoea (shortness of breath) (Lainchbury et al, 2003: Maisel et al, 2002: Mueller et al, 2004 cited also in Baggish et al, 2006) and also recommended in recent NICE guidelines.  However, other factors such as comorbid illnesses, age, renal failure and body mass may affect its NT-proBNP levels in way that can obscure the diagnosis particularly when the marker is used in isolation (Raymond et al. 2003 cited also in Baggish et al, 2006 and NICE guidelines).  Therefore it is essential that BNP is used as a tool to aid the diagnosis in addition to patients’ history and clinical symptoms.  Any doubt about BNP results and patients diagnosis can still result in patients being referred for further investigations.

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