At a Glance
Patients with heart failure (HF) present with symptoms of dyspnea and shortness of breath. A patient who presents to the emergency department with acute symptoms may have decompensated HF with excessive volume overload. The etiology of HF is coronary artery disease, hypertension, valve disease, or idiopathic. The differential diagnosis includes chronic obstructive pulmonary disease (COPD).
B-type natriuretic peptide (BNP) and N-Terminal (NT)-proBNP are biomarkers for HF, and either BNP or NT-proBNP should be measured in patients presenting to the emergency department with symptoms suggestive of HF. Increased levels of BNP or NT-proBNP are consistent with HF.
The diagnostic cut-off concentration for BNP is typically 100pg/mL. However, patients with renal and pulmonary disease can have intermediate values between 100 and 500pg/mL. The diagnostic cut-off for NT-proBNP is variable and age-dependent. Many laboratories use a cut-off of 125pg/mL for patients younger than 75 years of age and 450pg/mL for patients 75 years of age and older. However, other laboratories use higher cut-offs (e.g., <500pg/mL for patients younger than 50 years of age, <900pg/mL for patients younger than 75 years of age, and <1800pg/mL for patients 75 years of age and older).
Pro-BNP is the precursor protein to both BNP and NT-proBNP and originates from both the atrium and ventricles of the heart. Under physiologic conditions of volume overload, ventricular stretching and myocardial ischemia, pro-BNP is converted to these metabolites. BNP is the active metabolite and counteracts hypertension by stimulating vasodilation and the clearance of water and sodium. NT-proBNP is not biologically active. There is, essentially, no difference in the diagnostic value of BNP versus NT-proBNP. The choice of one assay over the other is determined by the availability of the specific instrumentation in use by the clinical laboratory.
Unlike acute coronary syndrome, which requires serial testing within a short time interval for diagnosis, HF is a chronic disease and only one sample is warranted at the time of admission. If a patient is diagnosed with decompensated heart failure, a second test after 1-2 days may be warranted to determine if diuretic therapy has been successful in compensating HF by lowering the BNP/NT-proBNP values. After the patient has stabilized, a third test may be indicated at the time of patient discharge to determine the baseline or “dry” weight BNP/NT-proBNP level. This may be useful in risk stratification of HF patients for future exacerbations.
Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?
Conditions other than HF can increase BNP and NT-proBNP, including age, renal failure and pulmonary disease, so results should be interpreted in the clinical context.
Drugs and herbal supplements do not affect BNP or NT-proBNP measurements.
What Lab Results Are Absolutely Confirmatory?
No laboratory result is absolutely confirmatory for HF.
BNP and NT-proBNP have been tested in large cohorts of high-risk patients without symptoms of HF but for whom follow-up data are available. The current evidence suggests that measuring BNP and NT-proBNP in asymptomatic patients is not cost-effective. International cardiology guidelines have suggested that echocardiography may be useful in screening asymptomatic patients for idiopathic HF, especially from first degree relatives with HF. These patients can be treated with angiotensin converting enzyme inhibitors if deemed necessary.
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- At a Glance
- Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?
- What Lab Results Are Absolutely Confirmatory?