Objective To examine the influence of obesity on the predictive value of the pro-B-type natriuretic peptide (NT-proBNP) assay in acute myocardial infarction.

Design Prospective observational study.

Setting All intensive care units in one region of France.

Patients 2217 consecutive patients admitted for an acute myocardial infarction matched with respect to age, gender, Killip class and renal function.

Main outcome measure Cardiovascular death at one year.

Results There were three groups (according to body mass index (BMI): obese, overweight and normal) of 739 matched patients. Median levels of NT-proBNP were considerably lower in high BMI patients, by about 20% in overweight and by 60% in obese patients, compared with normal BMI patients. An inverse relationship between the propeptide values and BMI was found in the overall study population (r=−0.20, p<0.0001), and for both genders. In multivariate linear regression, BMI as a continuous variable was a predictor of the log NT-proBNP level, even when adjusted for potential confounders. CV mortality at 1-year follow-up was similar for the three BMI groups (p=0.691). In multivariate logistic regression analysis, log NT-proBNP predicted mortality in normal (OR (95% CI) 3.48 (2.00 to 6.12)) and overweight (OR (95% CI) 3.96 (1.95 to 8.06)) patients, even when adjusted for confounders (GRACE risk score, left ventricular ejection fraction). However, in obese patients, propeptide levels failed to retain their independent prognostic value (OR (95% CI) 1.34 (0.86 to 2.08)).

Conclusions In this large population of patients with myocardial infarction, circulating NT-proBNP levels were considerably lower in obese patients; the significance of the propeptide level as an independent prognostic factor is severely compromised.