Pro B-type natriuretic peptide (proBNP) Test

Pro B-type natriuretic peptide (proBNP) is a protein that is produced by the heart when it is under stress. The proBNP test is a blood test that measures the level of proBNP in the blood.

There is no specific pre-test preparation required for the proBNP test. The test is typically done by drawing blood from a vein in the arm and sending it to a lab for analysis.

Common symptoms that may lead a healthcare provider to prescribe a proBNP test include shortness of breath, chest pain, fatigue, and swelling in the legs or feet. Individuals who have a history of heart disease, hypertension, or who have a family history of heart disease are at risk of having high proBNP levels and may need to be tested.

The test is used to diagnose and monitor heart failure, and to assess the severity of heart failure and to determine the effectiveness of treatment. High levels of proBNP can indicate heart failure, and low levels can indicate that the condition is under control.

The reference range for proBNP levels varies depending on the lab that is performing the analysis but generally, the normal range is considered to be less than 125 pg/mL. However, it is important to consult a healthcare professional for proper interpretation of the results, as other factors such as age, sex, and other medical conditions can affect proBNP levels.

It’s important to note that proBNP test is not a diagnostic test, it is only a screening test, and it should be used in conjunction with other diagnostic tests such as echocardiography and ECG to diagnose heart failure. Additionally, a positive screening test does not confirm the presence of heart failure, it only indicates that there is an increased risk and a diagnostic test is needed for a definitive diagnosis.

The ProBNP test measures the levels of B-type Natriuretic Peptide (BNP) or its precursor, N-terminal pro B-type Natriuretic Peptide (NT-proBNP), in the blood. These peptides are biomarkers released by the heart in response to stress and pressure changes, especially due to heart failure. Elevated levels of BNP or NT-proBNP in the blood can indicate heart failure and other cardiac conditions.

Why is the ProBNP Test Done?

The ProBNP test is used for several clinical purposes:

1. Diagnosing Heart Failure:
o Helps differentiate heart failure from other causes of similar symptoms, such as shortness of breath or fatigue.
2. Assessing the Severity of Heart Failure:
o Higher levels of BNP or NT-proBNP correlate with more severe heart failure.
3. Monitoring Treatment Response:
o Evaluates how well heart failure treatments are working over time.
4. Prognostic Indicator:
o Higher levels can indicate a worse prognosis in heart failure patients.
5. Screening for Cardiac Conditions:
o In patients at high risk of heart failure or with conditions that may lead to heart dysfunction.
6. Pre-Surgical Evaluation:
o Assessing cardiac risk in patients undergoing major non-cardiac surgery.

How is the ProBNP Test Performed?

The ProBNP test is a simple blood test. Here’s the process:

1. Preparation:
o Generally, no special preparation is required.
o Patients may be advised to avoid certain medications or foods that could affect the test results.
2. Sample Collection:
o Blood is drawn from a vein in the arm using a small needle.
o The blood sample is collected into a vial or test tube.
3. Laboratory Analysis:
o The blood sample is analysed in a lab to measure the levels of BNP or NT-proBNP.

Normal ProBNP Levels

The normal range for BNP and NT-proBNP varies depending on age, sex, and the specific assay used. However, typical reference ranges are:

• BNP:
o Generally, less than 100 pg/mL is considered normal.
o Levels above 400 pg/mL suggest heart failure.
• NT-proBNP:
o For patients under 50 years old: Less than 300 pg/mL.
o For patients 50-75 years old: Less than 900 pg/mL.
o For patients over 75 years old: Less than 1800 pg/mL.

These ranges can differ slightly based on the laboratory and the specific patient population being tested.

Factors Affecting ProBNP Levels

Several factors can influence BNP or NT-proBNP levels, including:

1. Heart Conditions:
o Heart Failure: Both acute and chronic heart failure can significantly elevate ProBNP levels.
o Atrial Fibrillation: Can cause moderately elevated levels.
o Valvular Heart Disease: Increases stress on the heart, raising ProBNP levels.
o Acute Coronary Syndromes: Myocardial infarction (heart attack) and unstable angina can elevate levels.
2. Other Medical Conditions:
o Kidney Disease: Reduced clearance of ProBNP, leading to higher levels.
o Pulmonary Diseases: Conditions like chronic obstructive pulmonary disease (COPD) can affect ProBNP levels.
o Liver Cirrhosis: Can alter ProBNP levels due to changes in blood volume and pressure.
o Obesity: Generally associated with lower BNP levels due to reduced cardiac stress markers.
3. Age and Gender:
o ProBNP levels naturally increase with age.
o Females tend to have higher levels than males.
4. Medications:
o Drugs like diuretics, ACE inhibitors, and beta-blockers can affect ProBNP levels.

Interpreting ProBNP Test Results

ProBNP test results must be interpreted in the context of the clinical presentation and other diagnostic findings. Here’s how elevated levels are generally understood:

1. Elevated Levels:
o Heart Failure: High levels strongly suggest heart failure. The higher the level, the more severe the heart failure is likely to be.
o Acute Coronary Syndrome: Elevated levels can indicate stress on the heart, common in heart attacks.
o Other Conditions: Conditions like renal failure or pulmonary hypertension can also elevate ProBNP levels.
2. Normal or Low Levels:
o Low levels make heart failure less likely, though they do not entirely rule it out.
o Normal levels in symptomatic patients might suggest non-cardiac causes of symptoms.

Clinical Context and Considerations

When interpreting ProBNP levels, consider the following:

1. Symptom Correlation:
o Match ProBNP levels with clinical symptoms like dyspnea, edema, or fatigue.
2. Other Diagnostic Tests:
o Use in conjunction with echocardiography, EKG, and clinical evaluation to assess heart function.
3. Chronic vs. Acute Conditions:
o Higher ProBNP levels in acute settings like decompensated heart failure versus chronic, stable conditions.
4. Non-Cardiac Causes:
o Elevated levels can occur in non-cardiac conditions; consider comprehensive clinical evaluation.

Follow-Up and Additional Testing

Based on ProBNP test results, further actions may include:

• Echocardiography: To visualise heart structure and function.
• Electrocardiogram (EKG): To assess electrical activity and identify heart rhythm problems.
• Chest X-Ray: To evaluate heart size and lung condition.
• Blood Tests: To check for markers of other conditions affecting heart function.
• Cardiac Stress Test: To assess heart function under stress.

Summary
The ProBNP test is a valuable tool for diagnosing and managing heart failure and other cardiac conditions. Understanding its role, normal ranges, and factors affecting levels can help in the accurate assessment and treatment of patients with suspected or confirmed heart disease.

References

• American Heart Association: NT-proBNP Test