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.

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 (> or =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 (> or =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.