Test Details: Natriuretic peptides are substances made by the heart. Two main types of these substances are brain natriuretic peptide (BNP) and N-terminal pro b-type natriuretic peptide (NT-proBNP). High levels can indicate that the heart is functioning inadequately and there is insufficient blood flow to the body organs. This condition is termed as congestive heart failure. Natriuretic peptide test measures the level of BNP or NT-proBNP in the individual's blood.