Interpreting BNP in patients with a history of HF
In patients presenting with acute dyspnea, is B-type natriuretic peptide testing less useful in patients with a history of heart failure?
A B-type natriuretic peptide (BNP) level of 100 pg/mL or greater in patients with a history of heart failure has a high sensitivity (100%), but a low specificity (41%), meaning it will misidentify heart failure as a cause of dyspnea in approximately 30% of patients. Increasing the cutoff to greater than 400 pg/mL increases the positive predictive value somewhat, but will miss some patients with heart failure as a cause. (LOE = 1c)
Chung T, Sindone A, Foo F, et al. Influence of history of heart failure on diagnostic performance and utility of B-type natriuretic peptide testing for acute dyspnea in the emergency department. Am Heart J 2006;152:949-955. [PMID:17070166]
Diagnostic test evaluation
BNP can diagnose heart failure in patients with acute dyspnea, usually using a cutoff value of at least 100 pg/mL to confirm the diagnosis. However, BNP levels in patients with chronic heart failure can be chronically elevated and thus may be elevated when the cause of dyspnea is other than heart failure (such as pulmonary embolism or pulmonary disease). The authors conducting this emergency department-based study enrolled 143 patients with dyspnea judged to require hospital admission. They excluded patients with acute coronary syndrome but did not describe how they selected patients to enter the study. Ideally, they would have enrolled patients consecutively who presented with the entrance criteria, but it appears they enrolled patients when it was convenient to do so, raising the possibility that these subjects are not representative of they typical patient with dyspnea. Blood was drawn for BNP determination and the emergency department physicians were asked to make a diagnosis before and, for 83 patients, following receipt of BNP results. The determination of heart failure as the cause of the dyspnea was made by a cardiologist following discharge of the patients. Patients with a history of heart failure had a median BNP of 729 pg/mL, whereas patients without a history had a median BNP of 217 pg/mL. Approximately 50% of the patients with dyspnea had a final diagnosis of heart failure as the cause. Using the standard cutoff, BNP in patients with a history of heart failure had a positive predictive value of 68% and a negative predictive value of 100%, meaning that it is effective at ruling out heart failure but will misidentify many patients as having heart failure who have another reason for their dyspnea. Increasing the cutoff from 100 pg/mL to 400 pg/mL in patients with a previous history of heart failure increases the positive predictive value to 77% but decreases the negative predictive value to 79%.
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