Brain Natriuretic Peptide, or BNP, is a protein hormone produced primarily by the heart’s lower chambers, the ventricles. Its measurement in the blood serves as a biomarker, providing a snapshot of the mechanical stress and strain placed on the heart muscle. When the ventricles are stretched excessively due to increased pressure or volume overload, they release BNP into the bloodstream. A related molecule, N-terminal pro-B-type natriuretic peptide (NT-proBNP), is released alongside BNP, and both are used in clinical practice to assess cardiac function.
The Role of BNP in the Body
The release of BNP is a protective mechanism activated in response to high pressure or fluid buildup in the heart. When the ventricular muscle fibers stretch, a precursor protein is cleaved, yielding the active BNP hormone and the inactive NT-proBNP fragment. BNP then acts as a chemical messenger, primarily targeting the kidneys and blood vessels to help reduce the heart’s workload.
In the kidneys, BNP promotes natriuresis, the excretion of sodium, and diuresis, the excretion of water, helping to eliminate excess fluid volume from the body. Simultaneously, the hormone causes vasodilation, or the widening of blood vessels. This action lowers blood pressure and reduces the systemic resistance the heart must pump against, helping to restore a healthier balance of fluid and pressure.
Interpreting Elevated Levels
The extent of the natriuretic peptide elevation is generally proportional to the severity of the underlying cardiac dysfunction. A significantly high number suggests more pronounced ventricular dysfunction. Clinical interpretation relies on established reference ranges, which vary depending on whether BNP or NT-proBNP is measured, as well as the patient’s age.
NT-proBNP levels tend to be higher than BNP levels because NT-proBNP is cleared primarily by the kidneys and has a longer half-life in the bloodstream. Active BNP, conversely, is cleared by enzymes and specific receptors. Clinicians use different thresholds for diagnosing acute versus chronic conditions, and these diagnostic cut-offs are often adjusted upward for older individuals.
Conditions That Cause Elevation
The most common and clinically significant cause of an elevated natriuretic peptide level is heart failure, where the heart cannot pump enough blood to meet the body’s needs. Both systolic heart failure, where the ventricle struggles to contract, and diastolic heart failure, where the ventricle struggles to relax and fill, result in the increased wall stress that triggers BNP release. The measurement is frequently used to help confirm this diagnosis when symptoms like shortness of breath are present.
However, an elevated BNP is not exclusively an indicator of heart failure, and several other conditions can cause a rise in the level. Other primary cardiac causes include acute coronary syndrome and valvular heart disease, which increase pressure within the chambers. Conditions that strain the right side of the heart, such as pulmonary embolism or pulmonary hypertension, also cause significant BNP elevation. Beyond the heart, kidney failure can elevate levels because NT-proBNP clearance is impaired, and severe infections like sepsis can cause a rise.
Using BNP to Guide Treatment
Once a cardiac condition, such as heart failure, is diagnosed, serial BNP or NT-proBNP testing becomes a tool for monitoring the effectiveness of medical therapy. The goal of treatment with medications like diuretics and vasodilators is to reduce the volume and pressure overload on the heart, which should lead to a measurable decrease in the natriuretic peptide level. A significant drop in the level over time suggests that the treatment regimen is successfully lowering ventricular wall stress.
Conversely, sustained high levels or a failure of the level to decline may signal that the current therapy is inadequate or that the disease is progressing. A persistently high or rising natriuretic peptide level carries prognostic value, correlating with an increased risk of future hospitalization or adverse outcomes. The measurement provides objective feedback that complements the assessment of a patient’s symptoms.