This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, 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: Plasma urea/creatinine ratio of 20:1 is seen in renal azotemia. In renal failure both BUN and creatinine levels are elevated, and the ratio is elevated as filtered urea is reabsorbed and creatinine is excreted. Ref: CURRENT Diagnosis & Treatmentchapter, Chapter 9; Advances in clinical chemistry, Volume 29 By Herbe E. Spiegel, Page 137; Nephrology in 30 Days By Robe F. Reilly, Mark A. Perazella, Page 234.