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) = %

Potassium :   Serum (PK) : mmol/L Urinary (UK) : mmol/L Osmolality :   Serum (POsm) : mOsm/L Urinary (UOsm) : mOsm/L   Transtubular Potassium    Gradient (TTKG) = %

Fractional Excretion of Sodium (FENa) = (UNa x PCr) / (PNa x UCr) x 100

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

Transtubular Potassium Gradient (TTKG) = (UK x Posm) / (PK x Uosm)

Interpretation of the Urinary Indices

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