From the Guidelines
BNP levels often do not correlate well with heart failure severity in obese patients due to the degradation of BNP by neprilysin, an enzyme produced by adipose tissue, leading to lower circulating BNP levels. This is supported by a study published in 2020 1, which highlights the importance of considering BMI when interpreting BNP levels. The study suggests that concentrations of natriuretic peptides are lower in obese patients, and several pathways have been proposed for this, including a bidirectional relationship between BNP and adiposity.
Key Factors Affecting BNP Levels in Obese Patients
- Adipose tissue produces neprilysin, an enzyme that degrades BNP, leading to lower circulating BNP levels in obese individuals even when they have heart failure
- Adipose tissue contains fewer natriuretic peptide receptors, resulting in reduced clearance of BNP from circulation
- The mechanical stress of obesity on the heart can lead to chronic BNP elevation, making acute changes less noticeable
- A study published in 2009 1 found that patients with a high BMI had lower BNP levels than those with a lower BMI, and that BMI affects the optimal prognostic threshold of BNP
Clinical Implications
- When interpreting BNP levels in obese patients, clinicians should use lower diagnostic thresholds (approximately 50% lower than standard cutoffs) and consider using NT-proBNP instead, which may be less affected by body mass, as suggested by the 2020 study 1
- Clinical assessment remains crucial, as relying solely on BNP values in obese patients may lead to underdiagnosis of heart failure
- The relationship between BNP and obesity demonstrates an "obesity paradox" where higher BMI is associated with lower natriuretic peptide levels despite increased cardiac stress, as noted in the 2009 study 1
Recommendations for Clinical Practice
- Consider the patient's BMI when interpreting BNP levels, and adjust diagnostic thresholds accordingly
- Use NT-proBNP instead of BNP in obese patients, if possible
- Combine BNP or NT-proBNP levels with clinical assessment to ensure accurate diagnosis of heart failure in obese patients, as recommended by the 2020 study 1
From the Research
B-type Natriuretic Peptide (BNP) in Obese Patients
- BNP levels are lower in obese patients with heart failure compared to non-obese patients 2, 3, 4, 5, 6
- The cause of this phenomenon is unclear, but it may be related to the inverse correlation between body mass index (BMI) and BNP levels 2, 6
- NT-proBNP, a related biomarker, also shows an inverse correlation with BMI 3, 4
Clinical Implications
- Caution should be exercised when interpreting BNP levels in obese patients, as they may not accurately reflect the severity of heart failure 2
- BMI-specific cutpoints may be necessary to optimize the sensitivity of BNP and NT-proBNP for diagnosing decompensated heart failure in obese patients 5
- NT-proBNP may be a stronger predictor of adverse cardiovascular events in both obese and non-obese patients 3, 4