BNP belongs to a family of protein hormones called natriuretic peptides. It is formed when its precursor, proBNP is proteolytically cleaved into BNP (biologically active) and NT-proBNP (not biologically active). Both BNP and NT-proBNP are released in response to changes in pressure inside the heart which can be related to heart failure and other cardiac problems. BNP is useful both in the diagnosis and prognosis of heart failure and is considered to be a gold standard biomarker in heart failure. Levels of BNP can be measured quantitively using a two-site sandwich ELISA or CLIA assay.