Laboratory Findings Distinguishing Acute Tubular Necrosis From Prerenal Azotemia

Rate of creatinine rise

0.3–0.5 mg/dL/day (26.5–44.2 micromol/L)

Variable and fluctuates

BUN/creatinine ratio

10–15:1

> 20:1

Urine osmolality (in mOsm/kg or mmol/kg)

< 450 (usually < 350)

> 500

Urine specific gravity

≤ 1.010

>1.020

Urine sodium (in mEq/L or mmol/L)

> 40

< 20

Urine/plasma creatinine ratio

< 20

> 40

Fractional excretion of sodium (%)

> 2

< 1

Urinary sediment

Muddy brown granular casts, epithelial cell casts, free epithelial cells, or a combination

Normal or with hyaline casts