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Table 3 Biochemical parameters in prerenal and renal AKI

From: Practical approach to detection and management of acute kidney injury in critically ill patient

Parameters Prerenal Renal Comments
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
  1. ATN acute tubular necrosis, FeNa fractional excretion of sodium, FeUrea fractional excretion of urea