• Jean-Sebastien Rachoin, Ralph Daher, Charles Moussallem, Barry Milcarek, Krystal Hunter, Christa Schorr, Mariam Abboud, Patricia Henry, and Lawrence S Weisberg.
• Division of Critical Care Medicine, Department of Medicine, Cooper University Hospital, Camden, NJ, USA.
• Nephrol. Dial. Transplant. 2012 Jun 1;27(6):2248-54.

Background And ObjectivesAcute kidney injury (AKI) is common in critically ill patients and is associated with a high mortality rate. Pre-renal azotemia, suggested by a high blood urea nitrogen to serum creatinine (BUN:Cr) ratio (BCR), has traditionally been associated with a better prognosis than other forms of AKI. Whether this pertains to critically ill patients is unknown.MethodsWe conducted a retrospective observational study of two cohorts of critically ill patients admitted to a single center: a derivation cohort, in which AKI was diagnosed, and a larger validation cohort. We analyzed associations between BCR and clinical outcomes: mortality and renal replacement therapy (RRT).ResultsPatients in the derivation cohort (N = 1010) with BCR >20 were older, predominantly female and white, and more severely ill. A BCR >20 was significantly associated with increased mortality and a lower likelihood of RRT in all patients, patients with AKI and patients at risk for AKI. Patients in the validation cohort (N = 10 228) with a BCR >20 were older, predominantly female and white, and more severely ill. A BCR >20 was associated with increased mortality and a lower likelihood of RRT in all patients and in those at risk for AKI, BUN correlated with age and severity of illness.ConclusionsA BCR >20 is associated with increased mortality in critically ill patients. It is also associated with a lower likelihood of RRT, perhaps because of misinterpretation of the BCR. Clinicians should not use a BCR >20 to classify AKI in critically ill patients.

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