What are BNP and NT-proBNP tests?

What are BNP and NT-proBNP tests?

BNP and NT-proBNP tests are used for detection of heart failure. When the heart fails, there is stretching of the lower muscular chambers known as ventricles. This leads to secretion of these substances from the heart muscle. 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. Peptides are made of amino acids bound in sequence. One end is known as amino terminal the other end is known as carboxyl terminal.

NT-proBNP stays in the blood for a longer period than BNP. Hence blood levels of NT-proBNP are more stable. Thus, it can reflect the stretching of the left ventricle, the lower left chamber over the previous 12 hours. This is the reason why NT-proBNP is tested more often than BNP for the detection of heart failure in the hospital. 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.

Values of this test can increase with age and kidney failure. Hence normal values are different for older persons compared to younger ones. As the values can be high in kidney failure even without heart failure, the use of BNP and NT-proBNP tests are limited in those patients.

Natriuretic means increasing the excretion of sodium in urine. It also increases the urine output. ANP is atrial natriuretic peptide, secreted from the upper chambers of the heart. BNP was initially identified in the brain of pigs and hence the name. Peptide is a chain of amino acids, with an NH₂ group at one end, known as amino terminal and COOH group at the other end, known as carboxyl terminal.