The initial primary use of measuring b-type natriuretic peptide (BNP) is to determine the etiology of dyspnea in patients presenting to the emergency department. If the BNP level is significantly elevated (greater than 400 pg/mL), heart failure is the likely diagnosis. Note that the degree of BNP elevation does not correlate with the severity of symptoms.

BNP levels are elevated in patients with atrial fibrillation and acute coronary syndromes as well, however it is not used to diagnose these conditions.

BNP levels play an important prognostic role in other cardiac conditions. Patients with high BNP levels during acute coronary syndromes or in the setting of severe valvular heart disease (aortic stenosis and/or mitral regurgitation) have a worse prognosis. Also, BNP levels are low in patients with heart failure from constrictive pericarditis which differentiates it from restrictive cardiomyopathy where the BNP levels are high.

A newer assay measuring NT-terminal pro-BNP (NT-proBNP) is more sensitive to detect heart failure and used in many institutions. The levels of BNP and NT-proBNP are essentially the same in normal individuals, but in the presence of heart failure the NT-proBNP is approximately four times higher than the corresponding BNP level, thus reducing the likelihood of a result in the ambiguous range (i.e. BNP level of 300 which is high, but not quite definite heart failure which would be > 400).