Acute Dyspnea: Diagnostic Role of the B-Natriuretic Peptide Assay
April 1, 2002 4 minutes read
Acute Dyspnea: Diagnostic Role of the B-Natriuretic Peptide Assay
Abstract & Commentary
Source: Morrison LK, et al. Utility of a rapid B-natriuretic peptide assay in differentiating congestive heart failure from lung disease in patients presenting with dyspnea. J Am Coll Cardiol 2002;39:202-209.
Acute shortness of breath is the usual chief complaint on emergency department (ED) presentation for both congestive heart failure (CHF) and pulmonary disease such as chronic obstructive pulmonary disease (COPD), pneumonia, and pulmonary embolism. Clinical history, examination, laboratory work-up, and even chest radiograph are often non-specific in differentiating CHF from pulmonary disease, particularly in the elderly and obese. This study investigates the utility of a rapid blood assay of B-type natriuretic peptide (BNP) in distinguishing CHF from other pulmonary causes of dyspnea.
BNP is a neuro-hormone natriuretic polypeptide secreted by cardiac ventricular tissue. Serum BNP levels have been demonstrated to rise proportionally with ventricular volume expansion and pressure overload, which occurs with acute CHF exacerbations.
In this investigational study, a convenience sample of 321 patients who presented to a Veterans Administration (VA) hospital urgent care center with a complaint of acute dyspnea had blood samples drawn for BNP measurements by means of a rapid, point-of-care assay kit and machine (Triage Biosite Diagnostics). Treating physicians were blinded to the results, and the diagnosis of CHF was based on independent, blinded review of the medical record by two cardiologists.
The investigators found a significantly higher mean BNP level (759 pg/mL) in patients with acute CHF (n = 134) than in those with pulmonary disease as a cause of their dyspnea (61 pg/mL, n = 85). This significant difference also was found in the subgroup of patients who had a history of both CHF and lung disease (such as COPD). In patients with acute CHF with a history of lung disease, mean BNP level was 731 pg/mL, whereas in patients with acute COPD exacerbations with a history of CHF, mean BNP level was only 47 pg/mL.
The diagnostic utility of BNP was assessed by multivariate analysis and receiver-operator characteristic (ROC) curves, demonstrating that BNP had high sensitivity, specificity, and accuracy for acute CHF. The authors report that a cutoff BNP value of 80 pg/mL had a 99% negative predictive value for CHF. In a regression analysis, the investigators reported that BNP levels provided meaningful diagnostic information beyond the standard clinical workup data and information obtained on the study population.
The authors conclude that a rapid BNP blood assay has excellent diagnostic utility in differentiating CHF from other pulmonary causes of dyspnea, even in patients with co-morbid conditions that make such diagnoses difficult in the acute setting.
Commentary by Theodore C. Chan, MD, FACEP
In previous studies, elevated BNP levels have been associated with both severity and prognosis in patients with left ventricular dysfunction.1,2 In this industry-sponsored study, a rapid, point-of-care BNP assay demonstrated excellent utility in discriminating CHF from pulmonary causes of dyspnea in patients presenting with acute shortness of breath.
While the mean BNP levels were elevated to a remarkable extent in CHF patients (759 vs 61 pg/mL), it is important to note that the standard deviation from the mean was quite large (± 798 pg/mL), suggesting that there was a wide range of BNP results in the CHF study population. Moreover, patients with pulmonary embolism or COPD resulting in cor pulmonale also had elevations in their BNP levels.
This study was conducted at a VA institution, primarily in men (95% of all subjects). Patients presenting with cardiac ischemia (unstable angina or acute myocardial infarction) were excluded. In fact, BNP can be a marker of necrosis and, thus, elevations may be seen in the setting of ischemia. In addition, elevations may be seen in patients with renal failure or those on dialysis without evidence of CHF.
Despite these limitations, this study does indicate that the BNP assay, along with clinical assessment and other standard diagnostic tools such as chest radiography, is of use in diagnosing acute CHF in patients with dyspnea. However, the authors themselves note that BNP is "not a stand-alone test." This same group recently has reported that elevated BNP levels had prognostic value in predicting subsequent CHF and cardiac events during the following six months.3 What remains to be determined is whether the diagnostic use of BNP is cost-effective and results in an improved clinical outcome when utilized as a point-of-care test in the ED setting.
References
1. Wallen T, et al. Brain natriuretic peptide predicts mortality in the elderly. Heart 1997;77:264-267.
2. Yamamoto K, et al. Clinical criteria and biochemical markers for the detection of systolic dysfunction. J Card Fail 2000;6:194-200.
3. Harrison A, et al. B-type natriuretic peptide protein predicts future cardiac events in patents present to the ED with dyspnea. Ann Emerg Med 2002;39:131-138.
Dr. Chan, Associate Clinical Professor of Medicine, Emergency Medicine, University of California, San Diego, is on the Editorial Board of Emergency Medicine Alert.
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