New studies on the diagnostic utility of B-type natriuretic peptide (BNP) come out almost daily. In the Patient-Oriented Evidence that Matters section of the October 2002 issue of The journal of family practice, Drs. O’Connor and Meurer1 reported on results from one of the largest and perhaps best designed study to assess use of the BNP test in more than 1500 patients presenting to emergency departments at 7 sites.2 Use of a rapid (15-minute) bedside assay provided support for the diagnosis of heart failure as the cause of acute dyspnea, with a BNP concentration of more than 100 pg/mL being strongly suggestive of heart failure.
As exciting as these results are, they need to be interpreted with caution. Approximately 5% of the patients in this study had a prior history of left ventricular dysfunction but the original investigators2 believed heart failure was not the cause of the acute dyspnea. The average BNP value in this group of patients was more than 300 pg/mL, ranging from less than 50 pg/mL to more than 1000 pg/mL. BNP results may be misleading in patients who present with acute dyspnea and have a prior history of left ventricular dysfunction, because BNP values may be chronically elevated (to well over 100 pg/mL) in this population. While it is true that the higher the BNP value, the more severe the degree of left ventricular dysfunction, overlap in BNP results in this particular study was great enough between severity groups to limit the diagnostic value of the relative amount of BNP elevation. Clearly, finding a very low BNP value (<50 pg/mL) in a patient with acute dyspnea has a high (>90%) diagnostic value for ruling out heart failure as the acute cause of dyspnea. More data are needed, however, before we can truly know how best to interpret an elevated BNP reading in the acute setting for patients in whom standard clinical bedside evaluation fails to provide clear directive on how to proceed with acute management.
Ken Grauer, MD,
Department of Community Health and Family Medicine,
University of Florida College of Medicine, Gainesville.
E-mail: grauer@chfm.ufl.edu.
Drs. O’connor and Meurer respond:
Dr. Grauer makes excellent points. The BNP test is of limited utility among patients with a previous history of heart failure. Although the test performed well in the diagnosis of ventricular myocardial dysfunction in most patients (overall accuracy 83%), it did not distinguish whether this condition was acute or chronic. BNP results should not replace, but may add to the information obtained through a good history and careful clinical evaluation.
John O’Connor, MD, and Linda Meurer, MD, MPH,
Department of Family and Community Medicine,
Medical College of Wisconsin, Milwaukee.
E-mail: joconnor@mcw.edu.