What are BNP and NT-proBNP tests? Cardiology Basics

What are BNP and NT-proBNP tests? Cardiology Basics

BNP and NT-proBNP tests are used for detection of heart failure. When the heart fails, there is stretching of the ventricles which leads to release of BNP from the myocardium. Pro BNP is the precursor of BNP, which is cleaved by enzymes to NT-proBNP and BNP. BNP stands for brain natriuretic peptide or B-type natriuretic peptide.  BNP is biologically active while NT-proBNP is not. NT stands for amino terminal of the protein.

NT-proBNP has a longer plasma half life than BNP. Hence levels of NT-proBNP are more stable. Thus, it can reflect the stretching of the left ventricle, over the previous 12 hours. This is the reason why NT-proBNP is tested more often than BNP for the detection of heart failure. These tests are useful in differentiating between breathlessness due to heart disease and lung disease in the emergency department. In many situations, it is difficult to differentiate between the two in a sick person coming to the emergency department just by physical examination.

Levels of BNP and NT-proBNP can increase with age and renal failure. Hence normal values are different for older persons compared to younger ones. As the values can be high in renal failure even without heart failure, the use of BNP and NT-proBNP tests are limited in those patients. Some studies have suggested that high levels of BNP in chronic kidney disease indicate both reduced clearance of BNP by the kidneys as well as a compromised cardiac function.

In obese patients, clinical findings, chest X-ray and even bedside echocardiography has limitations in the diagnosis of heart failure. Abdominal obesity can even cause orthopnea like presentation due to elevated levels of diaphragm. Hence we are more likely to look at BNP/NT-proBNP to establish heart failure in the emergency room. But there is a great limitation for these estimations as BNP levels may be low due to obesity. Association between obesity and low BNP is probably mediated by expression of natriuretic peptide clearance receptor (NPR-C) in adipose tissue.

Sacubitril/Valsartan is an Angiotensin II Receptor Blocker Neprilysin Inhibitor (ARNI), an important medication in our therapeutic armamentarium for management of heart failure. Will you estimate BNP or NT-proBNP if the person is on ARNI and why? The biomarker of choice in heart failure patient on ARNI would be NT pro-BNP. This because neprilysin breaks down BNP while NT-proBNP is not a substrate of neprilysin. As BNP degradation is prevented by ARNI, BNP levels rise, though one would have expected a fall due to improvement in heart failure.