From the Guidelines
A low BNP level is a strong indicator that heart failure is unlikely, and it can be used to rule out heart failure as the cause of symptoms with a high degree of accuracy. BNP is a hormone released by the heart when it's under stress, particularly when the heart chambers are stretched due to increased pressure or volume. When BNP levels are low (typically below 100 pg/mL), it indicates that the heart is not experiencing significant strain or volume overload, as noted in the European Society of Cardiology guidelines 1. This finding is particularly useful in clinical settings when evaluating patients with symptoms like shortness of breath, as it helps differentiate between cardiac and non-cardiac causes.
Key Points to Consider
- Low BNP has a high negative predictive value, meaning it's very good at ruling out heart failure as the cause of symptoms, as supported by a systematic review and diagnostic meta-analysis in the acute care setting 2.
- However, interpretation should always consider the clinical context, as some factors can cause falsely low BNP readings despite heart problems, including obesity, flash pulmonary edema (very acute heart failure), and certain types of heart failure with preserved ejection fraction.
- Additionally, BNP levels tend to be lower in patients taking medications like angiotensin receptor-neprilysin inhibitors (ARNIs).
- If a patient has symptoms suggesting heart failure but has a low BNP, clinicians should consider alternative diagnoses such as pulmonary conditions, anemia, or deconditioning.
Clinical Application
In clinical practice, a low BNP level can help clinicians quickly rule out heart failure and focus on other potential causes of symptoms, allowing for more efficient use of resources and potentially reducing mortality, as highlighted in the study published in the BMJ 2. However, it's essential to consider the pretest probability and interpret the result in the clinical context, taking into account factors that may affect BNP levels and considering further assessment with echocardiography or other cardiac imaging if necessary.
From the Research
Significance of Low BNP Levels
- Low BNP levels can be observed in patients with heart failure, despite expectations of high BNP levels in such conditions 3
- A study found that 4.9% of patients with hospitalized heart failure, 14.0% with abnormal cardiac structure or function, and 16.3% with abnormal hemodynamics had very low BNP levels (<50 pg/ml) 3
- Higher body mass index was found to be the strongest predictor of unexpectedly low BNP levels 3
- Low BNP levels have been associated with poor clinical outcomes in patients with chronic and advanced heart failure, potentially due to exhaustion of biosynthesis mechanisms 4
Clinical Implications
- Low NT-proBNP levels may be an early sign for the diagnosis of ischemic heart failure, particularly in patients with normal left ventricular ejection fraction (LVEF) in the early phases of acute heart failure hospitalization 5
- BNP-guided therapy has been shown to improve outcomes in heart failure patients, with a goal of decreasing BNP plasma levels <100 pg/ml 6
- A study found that BNP-guided strategy reduced the risk of heart failure-related death or hospital stay for heart failure, mainly through an increase in angiotensin-converting enzyme inhibitor and beta-blocker dosages 6