Clinical Investigations
Effect of body mass index on natriuretic peptide levels in patients with acute congestive heart failure: A ProBNP Investigation of Dyspnea in the Emergency Department (PRIDE) substudy

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Background

Obesity is associated with lower B-type natriuretic peptide (BNP) levels in healthy individuals and patients with chronic congestive heart failure (CHF). Neither the mechanism of natriuretic peptide suppression in the obese patient nor whether obesity affects natriuretic peptide levels among patients with acute CHF is known.

Methods

The associations of amino-terminal pro-BNP (NT-proBNP), BNP, and body mass index (BMI) were examined in 204 subjects with acute CHF. Multivariable regression analyses were performed to identify factors independently related to NT-proBNP and BNP levels.

Results

Across clinical strata of normal (<25 kg/m2), overweight (25-29.9 kg/m2), and obese (≥30 kg/m2) patients, median NT-proBNP and BNP levels decreased with increasing BMI (both P values < .001). In multivariable analyses adjusting for covariates known to affect BNP levels, the inverse relationship between BMI and both NT-proBNP and BNP remained (P < .05 for both). Using a cut point of 900 pg/mL, NT-proBNP was falsely negative in up to 10% of CHF cases in overweight patients (25-29.9 kg/m2) and 15% in obese patients (≥30 kg/m2). Using the standard cut point of 100 pg/mL, BNP testing was falsely negative in 20% of CHF cases in both overweight and obese patients. The assays for NT-proBNP and BNP exhibited similar overall sensitivity for the diagnosis of CHF.

Conclusions

When adjusted for relevant covariates, compared with normal counterparts, overweight and obese patients with acute CHF have lower circulating NT-proBNP and BNP levels, suggesting a BMI-related defect in natriuretic peptide secretion. NT-proBNP fell below the diagnostic cutoff for CHF less often than BNP in overweight and obese individuals; however, when used as a diagnostic tool to identify CHF in such patients, both markers may have reduced sensitivity.

Section snippets

Study sample

The details of the PRIDE study have recently been described.7 The study examined 600 patients with acute dyspnea to evaluate the role of NT-proBNP levels in the diagnosis of acute CHF. For each subject, a study physician was provided with all hospital records pertaining to the subject, starting from the time of emergency department presentation through to the results of the 60-day follow-up. These records included (when available) office notes, hospital discharge records, and results of all

Results

Overall, 59 (29%) participants were overweight, 64 (31%) participants obese, and 81 (40%) were normal. Body mass index ranged from 15.5 to 51.7 kg/m2 (mean ± SD = 27.6 ± 6.6 kg/m2). Morbidly obese patients (BMI >40 kg/m2) accounted for 14 (7%) of the 204 study subjects. Characteristics of the study sample by clinical strata of BMI are shown in Table I. Overweight and obese patients were younger, had higher creatinine clearance, and a higher prevalence of diabetes (all P < .05) than patients

Discussion

Obesity affects more than 40 million Americans, and between 280 000 and 325 000 deaths are attributed to obesity annually in the United States.20 Both figures are rapidly increasing. Obesity-related illnesses, such as diabetes and hypertension, are risk factors for CHF,1., 2., 3. which represents a major source of morbidity and mortality among overweight and obese patients. As overweight and obese patients with dyspnea are often the most difficult to assess clinically, BNP assays have the

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