FENa calculator

Fractional Excretion of Sodium (FENa)

FENa — Fractional Excretion of Sodium

Parameter	Value
Serum Sodium (mEq/L)
Serum Creatinine (mg/dL)
Urine Sodium (mEq/L)
Urine Creatinine (mg/dL)
FENa (%)	%

Interpretation (in setting of oliguria/AKI)
<1%	Pre-renal azotemia — Kidneys are sodium-avid (hypoperfusion, hypovolemia, heart failure, cirrhosis). Consider volume resuscitation.
>2%	Intrinsic renal disease — ATN, AIN, or glomerulonephritis. Kidneys unable to concentrate urine.
1–2%	Indeterminate — May be seen in early ATN or with mixed etiologies. Clinical correlation required.
Important Caveats
FENa is unreliable on diuretics — use FEUrea instead Low FENa (<1%) can be seen in contrast nephropathy, rhabdomyolysis, early obstruction Not validated in CKD patients

References
Espinel CH. The FENa test: use in the differential diagnosis of acute renal failure. JAMA. 1976;236:579-581. PMID 947239. Steiner RW. Interpreting the fractional excretion of sodium. Am J Med. 1984;77:699-702. PMID 6486145.