Fractional Excretion of Sodium

Sodium:  
Serum (PNa): mmol/L
Urinary (UNa): mmol/L
Creatinine:  
Serum (PCr): mg/dl
Urinary (UCr): mg/dl
 
Fractional Excretion of Sodium (FENa) = %
Renal Failure Index (RFI) = %
Fractional Excretion of Sodium (FENa) = (UNa x PCr) / (PNa x UCr) x 100

Renal Failure Index (RFI) = (UNa x PCr) / UCr

Interpretation of the Urinary Indices

  Prerenal ATN Postrenal
UNa (mmol/L) < 20 > 40 > 40
FENa < 1% > 1% > 4%
RFI < 1% > 1% > 1%

Google