|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|
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|