This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney and ureter, Subject name: Surgery
[{'content': 'A 65-year-old man has urine output of 10 mL/h following abdominal aoic aneurysmectomy. Acute tubular necrosis is suggested by the presence of which of the following? \nSelect and explain. \nA. Urine osmolality of more than 500 mOsm/kg, B. Urine sodium of more than 40 mEq/L, C. Fractional excretion of sodium of <1%, D. Blood urea nitrogen (BUN)-to-serum creatinine ratio (SCR) of more than 20', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Oliguria-Acute tubular necrosis -Intrinsic Renal Failures Prerenal Failures Intrinsic Renal Failures Urine osmolality (mOsm/kg) >500 <350 Urine sodium (mEq/L) <20 >40 Fractional excretion of sodium <1% >2% BUN/SCR >20 <10 Urine/PCR >40 <20', 'role': 'assistant'}]