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Serum Urea Nitrogen, Creatinine, and Estimators of Renal Function
Mortality in Older Patients With Cardiovascular Disease
Grace L. Smith, MD, MPH;
Michael G. Shlipak, MD, MPH;
Edward P. Havranek, MD;
JoAnne M. Foody, MD;
Frederick A. Masoudi, MD, MSPH;
Saif S. Rathore, MPH;
Harlan M. Krumholz, MS, MD
Arch Intern Med. 2006;166:1134-1142.
Background Renal dysfunction predicts increased mortality in cardiovascular patients, but the best renal estimator for quantifying risks is uncertain. We compared admission serum urea nitrogen (SUN) level, creatinine level, Modification of Diet in Renal Disease (MDRD) rate, and Mayo estimated glomerular filtration rate (eGFR) for predicting mortality.
Methods In a retrospective cohort of Medicare patients (aged  65 years) hospitalized for myocardial infarction (n = 44 437) and heart failure (n = 56 652), renal estimators were compared for linearity with 1-year mortality risk, magnitude of risk, and relative importance for predicting risk (percentage variance explained) in proportional hazards models.
Results The SUN level, creatinine level, and Mayo eGFR had linear associations with mortality. These measures predicted steadily increased risk in patients who experienced a myocardial infarction with a SUN level greater than 17 mg/dL (>6.1 mmol/L), a creatinine level greater than 1.0 mg/dL (>88.4 µmol/L), and a Mayo eGFR of less than 100 mL/min per 1.73 m2; and in patients who experienced heart failure with a SUN level greater than 16 mg/dL (>5.7 mmol/L), a creatinine level greater than 1.1 mg/dL (>97.2 µmol/L), and a Mayo eGFR of 90 mL/min per 1.73 m2 or less. In contrast, the MDRD eGFR had a J-shaped association and failed to identify increased risks in 50.0% of patients who experienced a myocardial infarction (with an MDRD eGFR >55 mL/min per 1.73 m2) and 60.0% of patients who experienced heart failure (with an MDRD eGFR >44 mL/min per 1.73 m2). The SUN level and Mayo eGFR had the greatest magnitude of risks. In myocardial infarction and heart failure patients, adjusted mortality increased by 3% and 7%, respectively, per 5-U increase in SUN, and by 3% and 9%, respectively, per 10-U decrease in Mayo eGFR (P<.001), based on models including both renal measures. Of all the measures, SUN had the greatest magnitude of relative importance for predicting mortality.
Conclusions In older cardiovascular patients, SUN- and creatinine-based measures were powerful predictors of postdischarge mortality. Only MDRD eGFR was less adequate in quantifying risks for patients with mild impairment. Novel estimators, such as the Mayo eGFR, may play an important role in outcomes' prognostication for these patients.
Author Affiliations: Section of Cardiovascular Medicine, Department of Internal Medicine (Drs Smith, Foody, and Krumholz and Mr Rathore), Department of Epidemiology and Public Health (Dr Krumholz), and Robert Wood Johnson Clinical Scholars Program (Dr Krumholz), Yale University School of Medicine, and Center for Outcomes Research and Evaluation, Yale–New Haven Hospital (Drs Foody and Krumholz), New Haven, Conn; General Internal Medicine Section, Medical Service, San Francisco Veterans Affairs Medical Center, San Francisco, Calif (Dr Shlipak); Departments of Medicine, Epidemiology, and Biostatistics, University of California, San Francisco (Dr Shlipak); Division of Cardiology, Denver Health Medical Center, and Divisions of Cardiology and Geriatric Medicine, University of Colorado Health Sciences Center, Denver, Colo (Drs Havranek and Masoudi); and Colorado Foundation for Medical Care, Aurora (Dr Masoudi).
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