In conjunction with an echocardiogram, BNP may become the gold standard for diagnosing diastolic dysfunction. As a screening test, BNP for HF may be more diagnostically helpful than the far-more-utilized prostate-specific antigen (PSA), Papanicolaou smears, or mammography used to screen for the corresponding prostate, cervical, and breast cancers. It has a high negative predictive value, meaning if the BNP value is low, this essentially rules out the presence of significant LVD. Therefore, it may preclude the need for an echocardiogram in patients with a very low value unless the test is necessary for other reasons. The potential diagnostic importance of the BNP in symptomatic patients presenting to the ED was recently published. This has significance because 80% of CHF emergency room visits yearly result in hospitalization. A test that assists with correct triaging of HF patients would be beneficial. In Maisal’s study, 1,586 patients presenting to the emergency department with dyspnea were evaluated in the usual manner. In addition, a BNP level was drawn with the ED doctors blinded to the results. Later, two cardiologists reassessed the patients’ records. They had access to all information: the ED records, results of diagnostic tests, such as echocardiograms, and data on hospital course, including response to treatment. The cardiologists then divided the patients into three groups: No HF, LVD without congestion, and LVD with congestion (CHF). The BNP levels were then unblinded. The results in Figure 4 demonstrate that BNP was able to significantly differentiate the patients in the three groups. Therefore, the ED physicians’ diagnostic accuracy can be enhanced by the availability of BNP measurements. In other studies, BNP is able to distinguish between those patients with dyspnea secondary to chronic obstructive pulmonary disease versus HF. And in the patients presenting with edema, a cardinal symptom of HF, BNP could make a distinction between those with and without CHF.
The BNP concentration increases as the pulmonary capillary wedge increases and, with treatment, the levels decrease temporally with the wedge pressure. The more severe the congestion, the higher the BNP level, and it strongly correlates with the NYHA functional classification. Tsutamoto et al. showed that BNP values provide prognostic information independent of other variables previously associated with a poor prognosis. When patients were stratified into two groups on the basis of median plasma concentration of BNP (73 pg/ml), the survival rates were significantly (p<0.0001) lower in patients with plasma BNP concentration of >73 pg/ml. Plasma BNP concentration was approximately five-fold higher in nonsurvivors than in survivors.
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As with several other diagnostic tests, the BNP is most useful when the pretest probability of the diagnosis is intermediate. For example, if the pretest probability is in the 50% range and the BNP level is 1,000 pg/ml, the post-test probability is increased to >90% range. Conversely, if in the same situation the BNP level is measured at 50 pg/ml, the post-test probability is reduced to approximately the 30% range. HF diagnosis nomograms have been developed based on this type of Bayesian analysis. The promising role of the BNP assay ranges from its potential as a screening tool for ALVD in high-risk patients, accurately diagnosing HF when patients present with nonspecific symptoms, such as dyspnea or edema, help with recognizing decompensations in known HF patients, to its possible use in predicting survival. Studies are currently underway to define its role in tailoring or guiding therapy.
Figure 4. Box Plots Showing Median Levels of B-Type Natriuretic Peptide Measured in the Emergency Department in Three Groups of Patients. Boxes show Interquartile ranges, and I bars represent highest and lowest values. NEJM. 2002:347:163.
Over 80% of patients presenting to the emergency room with symptoms suggestive of HF are admitted. Combine this information with the following HF readmission statistics: 2% of HF patients are readmitted within two days of discharge, 20% within one month, and 50% within six months. Innovative strategies are necessary in the approach to this disease. Attention to history and physical; prudent use of diagnostic tests; and an echocardiogram when indicated, including the two newer modalities—ICG and BNP—should positively affect the care of patients with HF starting with an improvement in the percentage of correct HF diagnosis.