Azotemia

What guidelines may distinguish acute tubular necrosis from prerenal azotemia?
Ans: In acute tubular necrosis, the fractional excretion of sodium (FENa) is >2, the fractional excretion of urea nitrogen is >50, the urinary sodium is >20 mmol/liter, and the ratio of urinary creatinine to plasma creatinine is <15.

In contrast, in prerenal azotemia, the fractional excretion of sodium (FENa) is <1,>20.

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New England Journal of Medicine - Vol. 359, No. 9, August 28, 2008