This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney, Subject name: Medicine
True about acute tubular necrosis - 
Select and explain. 
A. Urine specific gravity > 1.020, B. Urine osmolality > 300 mosmoles/kg, C. Urine Na< 1Omeq/L, D. Blood urea nitrogen :plasma creatinine ratio < 20
D: Blood urea nitrogen :plasma creatinine ratio < 20
Answer: D: Blood urea nitrogen :plasma creatinine ratio < 20 
Explanation: . A blood urea nitrogen (BUN)/creatinine ratio (BCR) >20 (0.081 in international unit) is used to distinguish pre-renal azotemia (PRA) and acute tubular necrosis (ATN). However, there is little evidence that BCR can distinguish between these two conditions and/or is clinically useful. Ref Harrison20th edition pg 278