FENa & Urine Indices Calculator

Fractional excretion of sodium, urine anion gap, and renal failure index for AKI workup.

Medical Disclaimer

This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.

Inputs

Urine Sodium (mEq/L)

Plasma Sodium (mEq/L)

Urine Creatinine (mg/dL)

Plasma Creatinine (mg/dL)

Urine Potassium (mEq/L)

Urine Chloride (mEq/L)

Tab to move between fields

Results

FENa

0.43%

Urine Anion Gap20 mEq/L

Renal Failure Index0.6

UCr/PCr Ratio66.7

How to Use This Calculator

Enter spot urine and plasma sodium (mEq/L) and creatinine (mg/dL) values.
Enter spot urine potassium (mEq/L) and chloride (mEq/L) for the urine anion gap.
Read the FENa (%): values <1% suggest pre-renal, 1-2% mixed, >2% intrinsic renal disease.
Review the urine anion gap: negative values suggest GI bicarbonate loss, positive values suggest renal tubular acidosis.
Use the renal failure index and UCr/PCr ratio to further differentiate acute kidney injury etiology.

How the result changes with Plasma Sodium (mEq/L)

Plasma Sodium (mEq/L)	FENa
108	0.56%
128	0.47%
152	0.4%
172	0.35%

What each input means

Urine Sodium (mEq/L): Spot urine sodium concentration.
Plasma Sodium (mEq/L): Serum sodium concentration.
Urine Creatinine (mg/dL): Spot urine creatinine concentration.
Plasma Creatinine (mg/dL): Serum creatinine concentration.
Urine Potassium (mEq/L): Spot urine potassium (for urine anion gap).
Urine Chloride (mEq/L): Spot urine chloride (for urine anion gap).

What each result means

FENa: <1% suggests pre-renal; 1-2% mixed; >2% intrinsic renal disease.
Urine Anion Gap: Negative = GI bicarb loss; Positive = renal tubular acidosis.
Renal Failure Index: RFI <1 suggests pre-renal; >1 suggests intrinsic renal.
UCr/PCr Ratio: Urine-to-plasma creatinine concentration ratio.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Urine Sodium (mEq/L) = 40, Plasma Sodium (mEq/L) = 140, Urine Creatinine (mg/dL) = 80, Plasma Creatinine (mg/dL) = 1.2 = 6 input(s) provided
Calculate FENa
FENa = (urineNa * plasmaCr) / (plasmaNa * urineCr) * 100
0.429 = 0.429
Calculate Urine Anion Gap
Urine Anion Gap = urineNa + urineK - urineCl
20 = 20
Calculate Renal Failure Index
Renal Failure Index = (urineNa * plasmaCr) / urineCr
0.6 = 0.6