FENa Calculator

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Choose the unit your lab report uses for creatinine. The calculator converts automatically.
Normal adult range: 136-145 mEq/L.
mEq/L
Spot urine sodium. Low values (under 20 mEq/L) suggest sodium conservation and prerenal physiology.
mEq/L
Elevated serum creatinine indicates reduced kidney clearance. Normal adult male: 0.6-1.2 mg/dL; female: 0.5-1.1 mg/dL.
mg/dL
Spot urine creatinine. Higher urine creatinine relative to serum creatinine reflects tubular concentration ability.
mg/dL
Blood urea nitrogen. Required to calculate FEUrea, which is preferred when the patient has taken diuretics.
mg/dL
Spot urine urea nitrogen. Required to calculate FEUrea.
mg/dL
FENaPrerenal
0.24%

Fractional excretion of sodium

Clinical interpretationPrerenal - sodium conservation intact (kidney underperfusion likely)
FEUrea23.33%
FEUrea interpretationPrerenal - suggests sodium conservation despite diuretics
0.24 %
Prerenal<1Indeterminate1-2Intrinsic / ATN2+

FENa is 0.24%, suggesting prerenal azotemia.

  • A FENa below 1% means the kidneys are avidly conserving sodium, consistent with reduced renal perfusion (volume depletion, heart failure, hepatorenal syndrome, or other prerenal states).
  • The tubules are functionally intact: they respond normally to decreased flow by reabsorbing sodium.
  • Important exception: early acute glomerulonephritis, contrast nephropathy, rhabdomyolysis, and myoglobinuria can also present with FENa below 1% despite intrinsic renal injury.
  • FEUrea is 23.33% (cut-off: 35%): supports prerenal physiology even if diuretics were given.

Next stepAssess volume status clinically (jugular venous pressure, skin turgor, orthostatic vitals) and review the medication list for nephrotoxins. If the patient has taken diuretics, interpret FEUrea instead.

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