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Table 138-2

Urine Diagnostic Indices in Differentiation of Prerenal Versus Intrinsic Renal Azotemia

Diagnostic IndexTypical Findings
Prerenal AzotemiaIntrinsic Renal Azotemia
Fractional excretion of sodium (%)a UNa × PCr/PNa × UCr × 100<1>1
Urine sodium concentration (mmol/L)<10>20
Urine creatinine to plasma creatinine ratio>40>20
Urine urea nitrogen to plasma urea nitrogen ratio>8<3
Urine specific gravity>1.018<1.015
Urine osmolality (mosmol/kg H2O)>500<300
Plasma BUN/creatinine ratio>20<10-15
Renal failure index UNa/UCr/PCr<1>1
Urinary sedimentHyaline castsMuddy brown granular casts

aMost sensitive indices.

Abbreviations: PCr, plasma creatinine concentration; PNa, plasma sodium concentration; UCr, urine creatinine concentration; UNa, urine sodium concentration.