Blood urea nitrogen has additive value beyond estimated glomerular filtration rate for prediction of long-term mortality in patients with acute myocardial infarction

Objectives: Blood urea nitrogen (BUN) has been shown to independently predict short- and intermediate-term outcomes in patients with acute myocardial infarction (AMI). We aimed to assess the additive predictive value of BUN beyond estimated glomerular filtration rate (eGFR) in AMI patients with an 8.6-year follow-up. Methods: This retrospective, observational single-centre study included 1332 consecutive AMI patients (median age 64 years, 58.4% male). BUN, creatinine and eGFR were determined at hospital admission. Results: During a median follow-up of 8.6 years (interquartile range [IQR] 4.0-11.6), 408 patients (30.6%) experienced the study endpoint of cardiovascular mortality. BUN (median 17.0 mg/dL [IQR 13.5-22.7]) was a significant predictor of cardiovascular mortality in univariate Cox regression (hazard ratio (HR) per 1 standard deviation increase 2.10, 95% confidence interval [CI] 1.94-2.28, p < .001). This association remained significant after multivariable adjustment for demographics, clinical variables and eGFR (adjusted HR 1.52 [CI 1.16-2.00, p = .003]). The association between BUN and outcome was more pronounced in patients with eGFR > 60 mL/min/1.73m(2) (HR 2.81 [CI 2.20-3.58, p < .001]). The discriminatory abilities (Harrell's C-statistic) for BUN, eGFR and creatinine were 0.75, 0.76 and 0.67, respectively. The addition of BUN to eGFR significantly improved the C-statistic (0.78, p for comparison = 0.017), net reclassification (23.7%, p < .001) and integrated discrimination (2.9%, p < .001). Conclusions: Circulating BUN on admission is an independent predictor of long-term cardiovascular mortality in AMI patients and adds predictive power beyond eGFR. BUN reflects not only kidney function, but also acute haemodynamic and neurohumoral alterations during AMI, and may help to identify high-risk patients.