Background: The blood urea nitrogen to creatinine ratio (BCR) has been used since the early 1940s to help clinicians\ndifferentiate between prerenal acute kidney injury (PR AKI) and intrinsic AKI (I AKI). This ratio is simple to use and often\nput forward as a reliable diagnostic tool even though little scientific evidence supports this. The aim of this study was\nto determine whether BCR is a reliable tool for distinguishing PR AKI from I AKI.\nMethods: We conducted a retrospective observational study over a 13 months period, in the Emergency Department\n(ED) of Nantes University Hospital. Eligible for inclusion were all adult patients consecutively admitted to the ED with a\ncreatinine >133 �¼mol/L (1.5 mg/dL).\nResults: Sixty thousand one hundred sixty patients were consecutively admitted to the ED. 2756 patients had plasma\ncreatinine levels in excess of 133 �¼mol/L, 1653 were excluded, leaving 1103 patients for definitive inclusion.\nMean age was 75.7 �± 14.8 years old, 498 (45%) patients had PR AKI and 605 (55%) I AKI. BCR was 90.55 �± 39.32 and 91.\n29 �± 39.79 in PR AKI and I AKI groups respectively. There was no statistical difference between mean BCR of the PR AKI\nand I AKI groups, p = 0.758. The area under the ROC curve was 0.5 indicating that BCR had no capacity to discriminate\nbetween PR AKI and I AKI.\nConclusions: Our study is the largest to investigate the diagnostic performance of BCR. BCR is not a reliable parameter\nfor distinguishing prerenal AKI from intrinsic AKI.
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