Impact of increased body mass index on accuracy of B-type natriuretic peptide (BNP) and N-terminal proBNP for diagnosis of decompensated heart failure and prediction of all-cause mortality.

BACKGROUND: BNP and N-terminal proBNP (NT-proBNP) concentrations may be depressed in patients with increased body mass index (BMI). Whether increased BMI affects accuracy of these biomarkers for diagnosing decompensated heart failure (HF) and predicting outcomes is unknown.
METHODS: We measured BNP and NT-proBNP in 685 patients with possible decompensated HF in a free-living community population subdivided by BMI as obese, overweight, and normal weight. HF diagnosis was adjudicated by a cardiologist blinded to BNP and NT-proBNP results. We tabulated all-cause mortality over a median follow-up of 401 days and assessed marker accuracy for HF diagnosis and mortality by ROC analysis.
RESULTS: Of the 685 patients, 40.9% were obese (n = 280), 28.2% were overweight (n = 193), and 30.9% had normal BMI (n = 212). Obese patients had lower BNP and NT-proBNP compared with overweight or normal-weight individuals (P < 0.001) and decreased mortality compared with normal-weight individuals (P < 0.001). Both biomarkers added significantly to a multivariate logistic regression model for diagnosis of decompensated HF across BMI categories. NT-proBNP outperformed BNP for predicting all-cause mortality in normal-weight individuals (chi(2) for BNP = 6.4, P = 0.09; chi(2) for NT-proBNP = 16.5, P < 0.001). Multivariate regression showed that both biomarkers remained significant predictors of decompensated HF diagnosis in each BMI subgroup.
CONCLUSIONS: In this study population, obese patients had significantly lower BNP and NT-proBNP that reflected lower mortality. BNP and NT-proBNP can be used in all BMI groups for decompensated HF diagnosis, although BMI-specific cutpoints may be necessary to optimize sensitivity.