Commentary

A test that could help establish the diagnosis of CHF in patients with dyspnea would be a boon to the clinician; such a test is described in the study by Maisel et al. Already shown to be useful in predicting functional capacity¹ and outcome² in patients with CHF, the bedside BNP assay was field tested in the toughest of proving grounds, the ED. How did it fare?

Quite well, judged against the final diagnosis of 2 independent cardiologists in possession of all clinical data available from the patient’s hospital encounter. Using a cut point of 100 pg/ml, the assay had 90% sensitivity and 76% specificity and contributed useful information when added to clinical data.

Could the study have used a better gold standard? An absolute standard for the diagnosis of CHF does not exist. Even if a pulmonary artery catheter is in place, it can be difficult to decide if rales are from CHF or atelectasis. The assay was superior to the validated Framingham and National Health and Nutrition Examination Survey Scores for establishing the diagnosis of CHF.

Another report from the same group³ shows how the BNP assay compares with the ED physician’s determination: It increased diagnostic accuracy by 7% and would have corrected the diagnostic impression a substantial number of times, even where the clinician was certain of the diagnosis. That same study also supplies a nomogram to calculate the probability of CHF given a BNP level and a pretest likelihood of CHF for those who prefer a quantitative approach to clinical decision making. One can only guess how much heparin, albuterol, or antibiotic would be saved if a reliable diagnosis of CHF could be made in the ED! Although it falls short of perfection, the BNP assay improves our ability to get this diagnosis right.