Table 3 Biochemical parameters in prerenal and renal AKI

Urine-specific gravity

> 1.020

1.008–1.012

In chronic kidney disease and renal AKI, urine-specific gravity is not reliable in the assessment of intravascular volume depletion due to lack of renal concentrating ability

BUN/Cr

> 20:1

10:1

In prerenal state, BUN is absorbed in proximal tubules out of proportion to GFR and serum creatinine, increasing the BUN/Cr ratio.

Caveats: Steroid therapy and low muscle mass can increase the ratio and decreased protein intake can lower the ratio.

Urine sodium

< 20 mEq/L

> 20 mEq/L

>20 mEq/L in ATN and diuretic therapy

FeNa

< 1.0%

> 2.0%

Caveats: Low FeNa is seen in contrast nephropathy, rhabdomyolysis, glomerulonephritis, vasculitis, and acute tubular necrosis (ATN) in the setting of cirrhosis and congestive heart failure. High FeNa (> 2.0%) is seen in AKI (e.g., ATN) and with diuretic use even in the setting of shock and hypovolemia

FeUrea

< 35%

> 50%

Useful in the setting of diuretic use