From the Guidelines
I would order BNP in a patient with leg swelling to support clinical decision making in the diagnosis of heart failure, especially when there is clinical uncertainty. BNP is a hormone released by the heart ventricles in response to stretching of heart muscle cells due to increased volume or pressure. Elevated BNP levels suggest heart failure as the cause of edema, while normal levels make heart failure less likely 1. This test is particularly useful when differentiating between cardiac and non-cardiac causes of leg swelling, such as distinguishing heart failure from conditions like venous insufficiency, lymphedema, or nephrotic syndrome. Some key points to consider when ordering BNP include:
- BNP testing should be interpreted alongside clinical findings, as levels can be affected by age, renal function, obesity, and certain medications 1.
- Values may be falsely elevated in patients with renal dysfunction and falsely low in obese patients.
- The test requires a simple blood draw and results are typically available quickly, making it a practical addition to the diagnostic workup for unexplained edema. In the context of heart failure diagnosis, BNP or NT-proBNP measurement is useful to establish prognosis or disease severity in outpatients with chronic heart failure, and can be useful in guiding therapy in select patients 1. However, it is essential to consider the clinical context and potential limitations of BNP testing when interpreting results.
From the Research
Reasons to Order BNP in a Patient with Leg Swelling
- Leg swelling can be a symptom of heart failure, and BNP levels can help diagnose this condition 2
- Elevated BNP levels are associated with cardiac valve regurgitation and myocardial damage, which can cause heart failure 2
- BNP levels can be used to rule out heart failure in patients with leg swelling, as low levels of BNP make heart failure unlikely 3
- In patients with acute myocardial infarction, BNP levels can be used to assess ventricular dysfunction and guide treatment 4
- BNP levels are part of the evaluation for patients with peripheral edema, and elevated levels may indicate heart failure 5
Clinical Significance of BNP Levels
- BNP levels can be increased in patients with heart failure, and the degree of elevation can correlate with the severity of the condition 2, 3
- BNP levels can be used to monitor the effectiveness of treatment for heart failure, such as angiotensin-converting enzyme inhibitors 4
- Elevated BNP levels can indicate cardiac dysfunction and increased risk of adverse outcomes in patients with cardiovascular disease 3, 6
Diagnostic Approach to Leg Swelling
- The evaluation of leg swelling should include a basic metabolic panel, liver function tests, thyroid function testing, BNP levels, and a urine protein/creatinine ratio 5
- Validated decision rules, such as the Wells and STOP-Bang criteria, can guide decision-making regarding the possibility of venous thromboembolic disease and obstructive sleep apnea 5
- Echocardiography should be performed in patients with pulmonary edema or elevated BNP levels to assess for heart failure 5