When Should I Order a BNP?

Abstract & Commentary

Synopsis: B-type natriuretic peptide (BNP) is a biomarker released by cardiac ventricular myocytes. Its usefulness is mainly in the emergency room for the evaluation of acute dyspnea, to evaluate for cardiac failure. BNP may have usefulness as a screening test for preclinical heart disease, for risk stratification and for guidance with therapy.

Sources: Mueller C, et al. N Engl J Med. 2004;350:647-654; Wang TJ, et al. N Engl J Med. 2004;350:655-663; Mark, DB. N Engl J Med. 2004;350:718-720.

Serum biomarkers provide a modern method of evaluating disease, and are especially used in cardiac disease. Cardiac troponins are useful in evaluating for acute coronary heart disease. The study by Mueller and colleagues, in Basel, Switzerland, shows how BNP both aids in diagnosis of acute dyspnea and saves money by screening out patients without heart failure. A BNP level of less than 100 pg per milliliter made the diagnosis of heart failure unlikely, while a level over 500 pg made it very likely.

For levels in between, clinical judgment using other criteria was required; 452 patients with acute dyspnea were randomized to receive a BNP level or not. Of the 225 patients getting a BNP, there were 10% fewer hospitalizations, and 9% fewer admissions to intensive care. BNP is a useful diagnostic test for acute congestive heart failure in emergency settings.

In the study by Wang and associates, 3346 adults without heart failure had a BNP level measured and were followed for about 5 years. This cohort came from the Framingham Offspring Study. Risk of death, heart failure, atrial fibrillation and stroke were increased with increasing BNP levels at screening (98% were below 80 pg per milliliter). It appears that BNP is a maker for risk of cardiac disease similar to levels of blood pressure.

Comment by Joseph E. Scherger, MD, MPH

I have had patients asking for BNP levels even before these studies were published based on press reports touting something like, "this new cardiac test may be the only test you need!" I wondered, what is this new test and is it really going to help me take better care of my patients? These studies help put serum BNP into perspective. Yes, the test is useful for patients with acute dyspnea. Is the dyspnea of pulmonary or cardiac origin? Having a definitive biomarker for heart failure is useful. For the patient in the office, getting a BNP level may just confirm what we already know. Risk of cardiac disease has many indications which are visible and measurable. More research needs to be done to help us understand the value of levels of BNP less than 100 pg per milliliter. For higher levels, the test may tell us we need to intensify our therapy for congestive heart failure. More research needs to be done to determine if we can use changing levels of BNP as a measure of the success of our therapy.

Dr. Scherger, Clinical Professor, University of California, San Diego, is Associate Editor of Internal Medicine Alert.