A 68-Year-Old Man Is Admitted to the Intensive Care Unit

A 68-year-old man is admitted to the intensive care unit after open abdominal aortic aneurysm repair. The patient has received 4 units of packed red blood cells during the surgery. During the first 24 hours following the procedure, he has only passed 200 mL of urine. He has congestive heart failure and hypertension. Laboratory results reveal elevated blood urea nitrogen.  The patient is given aggressive intravenous fluid hydration.  After 24 hours of therapy, urine output is increased and blood urea nitrogen declines toward normal.  Which of the following additional laboratory abnormalities suggests that this patient's initial oliguria is a compensation for volume contraction?

A) Muddy brown casts on urinalysis
B) Serum BUN/creatinine ratio <15
C) Urine fractional excretion of sodium >2%
D) Urine osmolarity <350 mOsm/kg
E) Urine sodium <20 mEq/L

Correct Answer:

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