What is a BNP (Brain Natriuretic Peptide) test?

BNP Test: A Diagnostic Tool for Heart Failure

The BNP (Brain Natriuretic Peptide) test is a blood test that measures levels of a hormone released by the heart ventricles in response to pressure and volume overload, primarily used to diagnose heart failure and assess its severity. 1, 2

What is BNP?

• BNP is a hormone primarily secreted by the cardiac ventricles in response to stretching of heart muscle cells due to increased volume or pressure 3
• It is synthesized as pre-proBNP, which is cleaved into proBNP, and then equimolarly cleaved into active BNP and NT-proBNP (N-terminal fragment) 3
• BNP exerts its biological actions through the NPR-A receptor, producing effects that counteract fluid expansion 3
• BNP is eliminated from circulation by neutral endopeptidases and clearance receptors (NPR-C) 3

Clinical Applications of BNP Testing

Diagnosis of Heart Failure

• BNP testing is most valuable in ruling out heart failure due to its high negative predictive value 1, 2
• BNP levels <100 pg/mL have a 94% negative predictive value for excluding heart failure 1, 4
• NT-proBNP levels <300 pg/mL have a 98% negative predictive value for excluding heart failure 1, 2
• BNP levels >400 pg/mL strongly suggest heart failure diagnosis with high positive likelihood ratio (>10) 2
• The "gray zone" (BNP 100-400 pg/mL) requires clinical correlation and additional testing 2

Specific Settings for BNP Testing

• Emergency department setting: BNP testing improves diagnostic accuracy in patients presenting with acute dyspnea 1, 5
• Ambulatory care setting: Helpful in confirming heart failure diagnosis in patients with ambiguous symptoms or confounding conditions like COPD 1
• Not recommended: For routine screening of asymptomatic populations or when clinical diagnosis is obvious 1

Interpretation Considerations

• BNP levels increase with age and are typically higher in women than men 3
• Obesity can lead to lower BNP levels, potentially masking cardiac dysfunction 2
• Renal dysfunction can elevate BNP levels due to decreased clearance 3
• Other conditions that can elevate BNP include pulmonary embolism, sepsis, and acute coronary syndromes 2, 6

Prognostic Value

• Elevated BNP levels correlate with increased mortality risk - for each 100 pg/mL increase in BNP, relative risk of death increases by approximately 35% 2
• BNP levels correlate with New York Heart Association (NYHA) functional classification of heart failure 4
• BNP is a strong predictor of risk of death and cardiovascular events in patients with established heart failure 4, 7

Treatment Monitoring

• BNP levels typically decrease with effective heart failure treatment including ACE inhibitors, ARBs, diuretics, and spironolactone 2, 4
• Rising BNP levels may indicate treatment failure or disease progression 2
• Patients with treated chronic stable heart failure may have BNP levels in the normal range 4

Common Pitfalls in BNP Testing

• BNP should not replace comprehensive clinical evaluation or imaging studies like echocardiography 1
• BNP levels may be in the "gray zone" in patients with stable but symptomatic chronic heart failure 1
• Correlation between BNP levels and hemodynamic parameters or ejection fraction is not always tight 1
• BNP testing should be considered as part of the diagnostic evaluation in heart failure, not the definitive diagnostic test 1

Testing Methods

• BNP and NT-proBNP are measured using automated rapid immunoassay techniques 3
• The FDA has approved the Triage BNP Test to aid in heart failure diagnosis 5