A few days after bilateral breast cancer excisions, your 69-year-old patient develops dyspnea on exertion. You know she has a history of chronic obstructive pulmonary disease (COPD), and on examination, you note rales, expiratory wheezing, and bilateral pedal edema. Her chest X-ray indicated mild pulmonary edema.
These signs and symptoms could result from COPD, pulmonary emboli, myocardial infarction, or heart failure. The quickest and surest way to determine if the cause is heart failure is to measure B-type natriuretic peptide (BNP).
What is BNP?
BNP is a neuroendocrine peptide synthesized in cardiac ventricular muscle. Both BNP and its inactive metabolite, the N-terminal portion (NT-proBNP), circulate in the plasma and can be easily measured.
The heart muscle continuously releases low levels of BNP and its counterpart in the atrial muscle, A-type natriuretic peptide (ANP). ANP is released in response to atrial stretch, and BNP is released in response to ventricular stretch. But many neuroendocrine and physiologic factors, including volume and pressure overload, can increase the rate of release.
The release of ANP and BNP causes vasodilation and inhibits aldosterone secretion from the adrenal gland and renin secretion from the kidney. The results: increased natriuresis and decreased blood volume, which decrease the signs and symptoms of heart failure.
Blood levels of BNP and NT-proBNP correlate well with left ventricular pressure, making them good markers for heart failure. The higher the levels, the more severe the heart failure.
Benefits of measuring BNP levels
The BNP and NT-proBNP tests are used in urgent care centers to aid in the differential diagnosis of dyspnea. If levels are elevated, dyspnea results from heart failure. If levels are normal, the cause of dyspnea isn’t cardiac. The test is particularly helpful when evaluating dyspnea in patients with both cardiac and chronic lung disease. (See BNP testing at a glance.)
Using BNP and NT-proBNP levels to rule out heart failure may spare the patient invasive and uncomfortable tests for heart failure, such as an echocardiogram and cardiac catheterization.
Some clinicians in acute medicine consider the BNP test to be the new standard in classifying the severity of heart failure because the degree of elevation correlates well with the New York Heart Association’s classification system.
BNP levels also help with the prognosis. If treatment for heart failure doesn’t rapidly return BNP levels to normal, the patient has a significantly higher risk of death in the months ahead.
BNP measurement is also evolving as an efficient, cost-effective screening technique for identifying patients with various cardiac abnormalities. For example, screening diabetic patients for high BNP levels to determine the risk of cardiac disease is becoming more common because the test costs so much less than an echocardiogram. Elevated BNP levels also appear in patients with prolonged systemic hypertension and patients with myocardial infarction.
What it takes
For BNP testing, you’ll collect a venous blood sample in an EDTA-containing tube (usually lavender-top). Some laboratories require an 8- to 12-hour fast. In a nonemergency situation, a physician may order cardiovascular drugs be withheld before the blood draw.
BNP levels are higher in elderly patients. The drug nesiritide (Natrecor), a recombinant form of the endogenous human BNP used to treat heart failure, increases BNP levels for several days.
Cardiac glycosides and diuretics can interfere with the accuracy of the test results. If the blood sample is drawn within 4 hours of the onset of acute symptoms, the results may be false-negative.Rapid, reliable tool
Heart failure has become a major health problem in the United States. Fortunately, in emergency and urgent situations, BNP testing offers a simple, inexpensive, reliable tool for rapid bedside detection.
Bhatia V, Nayyar P, Dhindsa S. Brain natriuretic peptide in diagnosis and treatment of heart failure. J Postgrad Med. 2003;49:182-185.
Januzzi JL, Camargo CA, et al. The N-terminal Pro-BNP investigation of dyspnea in the emergency department (PRIDE) study. Am J Cardiol. 2005:95:948-954.
Pagana K, Pagana T. Mosby’s Diagnostic and Laboratory Test Reference, 8th ed. St. Louis: Elsevier/Mosby; 2007.
Pagana K, Pagana T. Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Elsevier/Mosby; 2006.
Kathleen D. Pagana, PhD, RN, keynote speaker and author, is a Professor Emeritus at Lycoming College and President of Pagana Seminars & Presentations. She is the co-author of 18 books on diagnostic and lab testing. For more information about her presentations and books, contact her at www.kathleenpagana.com.