Clinical Investigation
Congestive Heart Failure
How obesity affects the cut-points for B-type natriuretic peptide in the diagnosis of acute heart failure: Results from the Breathing Not Properly Multinational Study☆

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Background

B-type natriuretic peptide (BNP) is valuable in diagnosing heart failure (HF), but its utility in obese patients is unknown. Studies have suggested a cut-point of BNP ≥100 pg/mL for the diagnosis of HF; however, there is an inverse relation between BNP levels and body mass index. We evaluated differential cut-points for BNP in diagnosing acute HF across body mass index levels to determine whether alternative cut-points can improve diagnosis.

Methods

The Breathing Not Properly Multinational Study was a 7-center, prospective study of 1586 patients who presented to the Emergency Department with acute dyspnea. B-type natriuretic peptide was measured on arrival. Height and weight data were available for 1368 participants. The clinical diagnosis of HF was adjudicated by 2 independent cardiologists who were blinded to BNP results.

Results

Heart failure was the final diagnosis in 46.1%. Mean BNP levels (pg/mL) in lean, overweight/obese, and severely/morbidly obese patients were 643, 462, and 247 for patients with acute HF, and 52, 35, and 25 in those without HF, respectively (P < .05 for all comparisons except 35 vs 25). B-type natriuretic peptide cut-points to maintain 90% sensitivity for a HF diagnosis were 170 pg/mL for lean subjects, 110 pg/mL for overweight/obese subjects, and 54 pg/mL in severely/morbidly obese patients.

Conclusions

Body mass index influences the selection of cut-points for BNP in diagnosing acute HF. A lower cut-point (BNP ≥54 pg/mL) should be used in severely obese patients to preserve sensitivity. A higher cut-point in lean patients (BNP ≥170 pg/mL) could be used to increase specificity.

Section snippets

Study population

The Breathing Not Properly Multinational Study was an international, 7-site (5 in the United States, 1 in France, and 1 in Norway), prospective study. Study design and main results have been published elsewhere.16 A total of 1586 patients were enrolled from April 1999 to December 2000. The study was approved by the institutional review boards of participating study centers, and written informed consent was obtained from all participants. To be eligible for the study, patients had to have

Results

The baseline characteristics of the entire Breathing Not Properly Multinational Study cohort have previously been reported.16 Among the 1368 patients with valid height and weight data, 526 were lean (BMI <25), 595 were overweight or obese (25 ≤ BMI < 35), and 247 were severely or morbidly obese (BMI ≥35). The range in BMI was 12.9 to 74.4, with a mean BMI for the population of 28.7 ± 8.3. The mean weight and BMI for patients within each subgroup is shown in Table I and did not vary among those

Discussion

Heart failure is a difficult diagnosis to make in the ED or urgent care setting.16, 24 Classic signs and symptoms are not always present. This is especially true in obese patients, whose body habitus may mask signs of edema and may muffle the heart and lung sounds during auscultation. For example, in our study, patients with higher BMIs were less likely to have documented murmurs or rales and were not as likely to have visible elevation of jugular venous pressure. History also can be less

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    Triage devices and meters and some financial support were provided by Biosite, San Diego, CA. Drs Nowak, Hollander, McCullough, and Maisel, and P Clopton have served as consultants and received research support from Biosite.

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