B-type Natriuretic Peptide (BNP)
BNP (B-type Natriuretic Peptide; synonymous to brain type natriuretic peptide) is a assay to assess for heart failure. Actually, BNP has been used in Europe for more than 10 years prior to their introduction in the United States in 2002. BNP, a 32 amino-acid proteohormone, is released from the heart chamber as a result of increased wall tension. Therefore, conditions that cause increased heart wall strain will result in increased levels of BNP in the blood. Conditions that can elevate BNP include heart failure, acute heart attack, hypertensive crisis, and even possibly right heart failure. This can now be detected by an assay or blood test. The BNP range is between 0 to >1500 nanograms/liter. Renal Failure can cause false elevations in BNP.
What is BNP useful to diagnose?
- BNP can help diagnose heart failure when a patient presents to the Emergency Room or Doctors Office with complaints of “shortness of breath.” BNP is able to distinguish shortness of breath from heart failure from other reasons for shortness of breath (emphysema, asthma, anxiety, etc.). A BNP level of 100ng/l, the shortness of breath is probably due to heart failure >70% of the time.
- BNP may be useful to help determine when to intervene in valve disorders (Aortic stenosis or Mitral regurgitation). BNP can be elevated with valvular disease even without experiencing symptoms. Because valve replacement surgery is considered major surgery and because other issues such as post-valve replacement blood thinning may be required, the timing of the valve surgery becomes crucial. If the valve surgery is deferred too long, then heart dysfunction may become so bad that valve surgery would no longer be tolerated by the patient. Although the studies involved only small numbers of patients (thus reducing statistical significance), elevated BNP levels in patients with valvular disorders may guide your cardiologist as to when to proceed with valve replacement or repair.
Can BNP be used to monitor how a patient’s heart failure is doing from one point in time to another?
Initial studies in Europe indicate that BNP can be used to track the effectiveness of treatment.
Can BNP be used to diagnose heart failure that arises due to inability of the heart to relax (diastolic dysfunction)?
There are some studies that suggest this can be done but the potential confounding problems is the presence of concomitant systolic dysfunction which can also be detected by elevated BNP. Elevated BNP levels in a patient with a normal left ventricle may correlate with diastolic dysfunction or even Right Ventricular dysfunction. Usually BNP do not rise over 700 ng/l when due to the latter two reasons. More studies need to be performed to confirm the usefulness of BNP in diagnosis of diastolic dysfunction.
BNP has also been used as a marker for ischemia (heart not getting enough blood). BNP has to be used in the clinical setting of a person having chest pain. Elevated BNP levels in this setting place patients with chest pain in a higher risk subcategory which means they require more prompt treatment with more aggressive measures (such as cardiac angiography) vs those patients with chest pain who don’t have elevated BNP.