From the Guidelines
Yes, BNP levels can be falsely low in obese individuals, and clinicians should use lower diagnostic thresholds when interpreting BNP results in these patients. This phenomenon occurs because adipose tissue contains natriuretic peptide receptors and neutral endopeptidases that clear BNP from circulation, leading to lower measured levels despite the presence of heart failure or other cardiac conditions 1. Obesity creates a state of relative natriuretic peptide deficiency, with studies showing that for the same degree of heart failure, obese patients typically have BNP levels 30-50% lower than their normal-weight counterparts.
Some key points to consider:
- BNP levels are lower in obese patients with heart failure compared to non-obese patients with heart failure 1
- The use of lower diagnostic thresholds for BNP in obese patients can help prevent missed diagnoses of heart failure 1
- NT-proBNP is also affected by obesity, although to a lesser extent than BNP 1
- Clinicians should consider the patient's BMI when interpreting BNP and NT-proBNP results, and adjust the diagnostic thresholds accordingly 1
For example, while a BNP cutoff of 100 pg/mL might be appropriate for normal-weight individuals, a threshold of 50-70 pg/mL may be more appropriate in those with BMI >30 kg/m². This adjustment helps prevent missed diagnoses of heart failure in obese patients. The same principle applies to NT-proBNP, another cardiac biomarker affected by obesity, though to a somewhat lesser extent 1.
It's also important to note that the relationship between obesity and BNP levels is complex, and other factors such as age, sex, and comorbidities can also influence BNP levels 1. However, the use of lower diagnostic thresholds for BNP in obese patients is a practical approach to help prevent missed diagnoses of heart failure in this population.
From the Research
Brain Natriuretic Peptide (BNP) Levels in Obesity
- BNP levels can be falsely low in patients with obesity, as observed in several studies 2, 3, 4, 5, 6.
- The cause of this phenomenon is unclear, but it is thought to be related to a defect in natriuretic peptide secretion in obese patients 5.
- Studies have shown that BNP levels decrease with increasing body mass index (BMI) 3, 5, 6.
- In patients with acute heart failure, BNP levels were lower in those with a higher BMI, regardless of whether they had preserved or reduced ejection fraction 3, 6.
- The use of BNP as a diagnostic tool may have reduced sensitivity in obese patients, as a significant proportion of patients with heart failure may have BNP levels below clinically accepted thresholds 5, 6.
- It is recommended to exercise caution when interpreting BNP levels in obese patients, as normal values may need to be adjusted according to the degree of obesity and heart failure stage 2, 4.
Clinical Implications
- Lower BNP levels in obese patients may lead to underdiagnosis or delayed diagnosis of heart failure 3, 5.
- The inverse relationship between BNP levels and BMI may affect the prognostic value of BNP in obese patients 6.
- Further research is needed to understand the mechanisms underlying the decrease in BNP levels in obese patients and to develop strategies for improving the diagnosis and management of heart failure in this population.
Study Findings
- A study published in 2009 found that obese patients with heart failure had lower BNP levels compared to non-obese patients, despite having similar severity of heart failure 2.
- A 2024 study found that BNP levels were lower in obese patients with acute heart failure and preserved ejection fraction, highlighting the need to lower the threshold of BNP levels in this population 3.
- Another study published in 2017 found that natriuretic peptides, including BNP, had a lipolytic action and that low levels of these peptides could contribute to obesity and hypertension 4.