Units: US SI

Fractional Excretion of Sodium (FENa)

Serum Na mEq/L
Urine Na mEq/L
Serum Cr mg/dL
Urine Cr mg/dL
FENA %

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

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

Prerenal: Anything that causes decreased effective renal perfusion: Hypovolemia, CHF, Renal Artery Stenosis, Sepsis, etc. Remember, contrast-induced nephropathy will often look pre-renal.

Intrinsic Renal: ATN, AIN, Glomerulonephritides, etc

Postrenal: Obstruction (BPH, bladder stone, bilateral ureter obstruction)

Posted in: Critical Care • Nephrology • Renal

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