BNP and NT-proBNP are measured by
immunoassay. Immunoassays use antibodies that bind to a specific part of the molecule to test for. Antibodies are only able to determine the amount of peptides matching their
epitope fragments. They largely cannot differentiate between a cleaved part and the uncleaved precursor. For example, a BNP antibody is likely to cross-react to proBNP but not NT-proBNP.
Interpretation of BNP Utility • The main clinical utility of NT-proBNP is that a normal level helps to rule out chronic heart failure in the emergency setting. An elevated NT-proBNP should never be used exclusively to "rule in" acute or chronic heart failure in the emergency setting due to lack of specificity . • Either BNP or NT-proBNP can also be used for screening and prognosis of heart failure. • Increased NT-proBNP adjusted for age and sex and annual increase of NT-proBNP above 50% are associated with increased event rate in patients with non-severe aortic valve stenosis. • BNP and NT-proBNP are also typically increased in patients with left ventricular dysfunction, with or without symptoms (BNP accurately reflects current ventricular status, as its half-life is 20 minutes, as opposed to 1–2 hours for NT-proBNP). A preoperative BNP can be predictive of a risk of an acute cardiac event during vascular surgery. A
cutoff of 100 pg/ml has a
sensitivity of approximately 100%, a
negative predictive value of approximately 100%, a
specificity of 90%, and a
positive predictive value of 78% according to data from the
United Kingdom. There is a diagnostic 'gray area', often defined as between 100 and 500 pg/mL, for which the test is considered inconclusive, but, in general, levels above 500 pg/ml are considered to be an indicator of heart failure. This so-called gray zone has been addressed in several studies, and using clinical history or other available simple tools can help make the diagnosis. Some laboratories report in units ng per Litre (ng/L), which is equivalent to pg/mL. BNP has been suggested as a predictor for a variety of
medical states, including cardiovascular mortality in diabetics and cardiac impairment in cancer patients. BNP was found to have an important role in prognostication of heart surgery patients and in the emergency department. It has been shown that combining BNP with other tools like
impedance cardiography (ICG) can improve early diagnosis of heart failure and advance prevention strategies. Utility of BNP has also been explored in various settings like
preeclampsia,
intensive care, shock and
end-stage renal disease (ESRD). The BNP test is used as an aid in the diagnosis and assessment of severity of heart failure. A recent meta-analysis concerning effects of BNP testing on clinical outcomes of patients presenting to the emergency department with acute dyspnea revealed that BNP testing led to a decrease in admission rates and decrease in mean length of stay, although neither was statistically significant. Effects on all cause hospital mortality was inconclusive. The BNP test is also used for the risk stratification of patients with acute coronary syndromes.
Factors that affect the typical range The effect or race and gender on value of BNP and its utility in that context has been studied extensively. BNP is cleared by binding to natriuretic peptide receptors (NPRs) and neutral endopeptidase (NEP). Less than 5% of BNP is cleared renally. NT-proBNP is the inactive molecule resulting from cleavage of the prohormone Pro-BNP and is reliant solely on the kidney for excretion. The "Achilles' heel" of the NT-proBNP biomarker is the overlap in kidney disease in the heart failure patient population: kidney disease patients remove NT-proBNP slower than usual, making an elevated value hard to interpret. When interpreting an elevated BNP level, values may be elevated due to factors other than heart failure. Lower levels are often seen in obese patients. Higher levels are seen in those with renal disease, in the absence of heart failure. == Therapeutic application ==