NT-proBNP is a BNP fragment (natriuretic peptide), a hormone secreted by the heart to help transport blood throughout the body. BNP is produced by the left ventricle, the heart’s main pumping chamber. The heart releases more BNP and NT-proBNP when the left ventricle is distended from working too hard, as in heart failure. Levels of NT-proBNP help diagnose and estimate the severity of heart failure. The test is particularly useful in hospital emergencies to help distinguish heart failure from severe lung damage, which often has the same symptoms. In an outpatient setting, the test is useful for monitoring disease progression and the effects of treatment.
Levels of NT-proBNP below 300 nanograms per litre (ng/L) indicate that heart failure is highly unlikely. Levels above 350 ng/L in individuals under 50 years of age, above 450 ng/L for individuals between 50 and 75 years of age or above 950 ng/L in individuals over 75 years of age are consistent with heart failure. Intermediate levels for each age group indicate that heart failure is unlikely, but they do not completely rule out the possibility.