B-type natriuretic peptide (BNP) is a hormone released into the bloodstream when the heart is overworked. A blood test measuring BNP levels provides information about how hard the heart is working and can offer insight into heart health and mortality risk.
What BNP Levels Indicate
BNP is produced by the heart’s ventricles in response to being stretched. The hormone acts on blood vessels to help them relax and on the kidneys to remove salt and water. This process helps lower blood pressure and reduce strain on the heart. The concentration of BNP is measured in picograms per milliliter (pg/mL).
A BNP level below 100 pg/mL is considered normal. Levels between 100 and 400 pg/mL may indicate some degree of heart strain and require further evaluation. A level above 400 pg/mL is considered high and suggests the presence of heart failure. Extremely high levels can reach several thousand pg/mL.
Another related marker, NT-proBNP, is an inactive fragment also released from the heart to assess cardiac stress. For individuals under 75, a normal NT-proBNP level is below 125 pg/mL, while for those over 75, it is under 450 pg/mL. Both tests provide similar information about heart function and help diagnose and manage heart-related conditions.
BNP as a Prognostic Marker for Heart Failure
The most frequent application of the BNP test is in diagnosing and assessing the severity of heart failure. This condition occurs when the heart cannot pump enough blood to meet the body’s needs. As heart failure progresses, the strain on the ventricles increases, leading to a rise in BNP production. Higher BNP levels are therefore associated with more severe heart failure.
BNP is a prognostic marker, with a strong correlation between elevated concentrations and mortality risk in patients with heart failure. Research indicates that for every 100 pg/mL increase in BNP, the risk of death increases by 35 percent. A patient’s BNP level can be a stronger predictor of mortality than traditional factors like age or the heart’s ejection fraction.
BNP itself is not the cause of death but a signal of cardiac distress. A high BNP level, such as one over 480 pg/mL, is associated with a higher probability of hospitalization or death within six months for patients with heart failure. When heart failure treatment is effective, BNP levels decrease, indicating a more stable condition and a better prognosis.
Other Conditions Affecting BNP Levels
While strongly associated with heart failure, elevated BNP levels are not exclusive to this condition. Other medical issues can cause the heart to work harder or affect how BNP is cleared from the body. Recognizing these other causes is important for an accurate diagnosis.
Several conditions can raise BNP levels:
- Kidney disease can cause an accumulation of BNP because the kidneys are responsible for filtering it from the blood.
- Pulmonary embolism (a blood clot in the lungs) puts strain on the right side of the heart.
- Chronic obstructive pulmonary disease (COPD) also strains the right side of the heart.
- High blood pressure (hypertension) can lead to an increase.
- Liver cirrhosis is another condition that may cause an increase.
Interpreting BNP in Context
A BNP level is never interpreted in isolation. Physicians consider the result alongside a patient’s symptoms, such as shortness of breath or swelling, and findings from a physical examination. This information is integrated with the patient’s age, sex, body weight, and other lab results, particularly those related to kidney function.
Imaging studies, like an echocardiogram, are often used to confirm a diagnosis by providing a view of the heart’s structure and function. If a patient has high BNP levels but a normal echocardiogram, a physician will investigate other non-cardiac causes. The goal of treatment is to address the underlying condition stressing the heart, not simply to lower the BNP number.