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
Plasma urea / creatinine ratio of 20:1 may be seen in- 
Select and explain. 
A. Rhabdomyolysis, B. Ureteric calculi, C. Pre-renal failure, D. Chronic glomerulonephritis
C: Pre-renal failure
Answer: C: Pre-renal failure 
Explanation: Background. 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 299