Definition
- Other names include B-type natriuretic peptide, N-terminal pro b-type natriuretic peptide, and NT-proBNP. BNP is a hormone secreted by myocytes in the ventricles (left ventricle) in response to pressure overload/myocyte stretch, with potent diuretic, natriuretic, and vascular smooth muscle relaxing effects. The heart normally produces low levels of a precursor protein, pro-BNP, which is cleaved to release the active hormone, BNP, and an inactive fragment, NT-proBNP.
- Normal range:
- BNP: <100 pg/mL
- NT-proBNP: 0 " “74 years of age: ≤124 pg/mL; 75 years of age and older: ≤449 pg/mL
Use
- Screening and diagnosis of CHF: BNP and NT-proBNP levels in the blood may be useful to establish prognosis in heart failure because both markers are typically higher in patients with worse outcome.
- Reading >480 pg/mL = 51% chance of cardiac/noncardiac events in next 6 months.
- Reading <230 pg/mL = 2.5% chance of cardiac/noncardiac events in next 6 months.
- Reading >130 pg/mL = 19% chance of sudden death.
- Reading <130 pg/mL = 1% chance of sudden death.
- Differential diagnosis of dyspnea: Readings <100 pg/mL rule out CHF as cause of dyspnea, and readings >400 pg/mL indicate a 95% likelihood of CHF. Readings between 100 and 400 pg/mL warrant further workup.
- Determination of severity of CHF: Higher values correlate with increasing New York Heart Association classes I " “IV. BNP is a prognostic tool for classes III and IV.
- Diagnosis of left ventricular dysfunction: Routine testing is not recommended for screening asymptomatic patient populations for left ventricular dysfunction. Increase in BNP in right heart failure is less than in left ventricular dysfunction.
- At appropriate cutoff values, BNP and NT-proBNP have similar S/S = 70%/70% and NPV = 80%.
- Greater increases predict worse adverse outcomes in patients with CHF.
- Increased values after acute myocardial infarction predict poorer prognosis.
- BNP increases with arrhythmias that are less marked.
- BNP and NT-proBNP can be increased in renal failure, especially if dialysis is needed.
- Abnormal echocardiogram without symptoms: mean value = 300 pg/mL.
Interpretation
Increased In
- Heart failure
- Left ventricular dysfunction
- Renal impairment
- Coronary artery disease
- Valvular disease
- Arrhythmias
- Brain injury
- Anemia (BNP)
- Sepsis and shock (NT-proBNP)
Limitations
- Routine blood BNP or NT-proBNP testing is not justified for determining specific therapy for patients with chronic or acute heart failure.
- Nesiritide (human recombinant BNP) increases BNP. Studies indicate a minimal effect on NT-proBNP.
- Age and exercise also increase BNP.
- Obesity decreases BNP.
- Intraindividual variation (approximately 50% and 60%, respectively, for BNP and NT-proBNP from week to week) indicates altered cardiac status.
Suggested Readings
1Apple ‚ FS, Wu ‚ HB, Jaffe ‚ AS National Academy of Clinical Biochemistry and IFCC Committee for Standardization of Markers of Cardiac Damage Laboratory Medicine Practice Guidelines: Analytical issues for biomarkers of heart failure. Circulation. 2007;226:e95 " “e98. 2Steiner ‚ J, Guglin ‚ M. BNP or NTproBNP? A clinicians perspective. Int J Cardiol. 2008;129(1):5 " “14. 3Tang ‚ WH, Francis ‚ GS, Morrow ‚ DA National Academy of Clinical Biochemistry Laboratory Medicine: National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: clinical utilization of cardiac biomarker testing in heart failure. Circulation. 2007;116(5): e99 " “e109.