Fractional Excretion of Sodium Calculator

The fractional excretion of sodium calculator helps you find FENa fast. FENa shows how much filtered sodium leaves the body in urine. It uses urine sodium, serum sodium, urine creatinine, and serum creatinine.

We developed this calculator so users can easily calculate fractional excretion of sodium without doing hard math by hand.

What Is Fractional Excretion of Sodium?

FENa is a kidney-related calculation. It compares sodium in urine with sodium in blood. It also uses creatinine to adjust the result.

The answer is shown as a percent. Doctors may use FENa when reviewing acute kidney injury. Still, FENa should not be used alone. Some drugs and kidney problems can affect the result.

Fractional Excretion of Sodium Formula

The core fractional excretion of sodium formula is:

FENa (%) = (Urine Sodium × Serum Creatinine) ÷ (Serum Sodium × Urine Creatinine) × 100

The same creatinine unit should be used for both values. This formula uses spot urine and blood values. It does not need urine volume.

How to Use Online Fractional Excretion of Sodium Calculator

1. Enter the urine sodium value in mmol/L.
2. Enter the serum sodium value in mmol/L.
3. Enter the urine creatinine value.
4. Enter the serum creatinine value. Use the same unit for both creatinine values.
5. Click the calculate button. The tool will show your FENa as a percent.

Example Fractional Excretion of Sodium Calculation

Let's use these sample values:

Urine sodium = 20 mmol/L

Serum sodium = 140 mmol/L

Urine creatinine = 100 mg/dL

Serum creatinine = 2 mg/dL

First, multiply urine sodium by serum creatinine:

20 × 2 = 40

Next, multiply serum sodium by urine creatinine:

140 × 100 = 14,000

Now apply the FENa formula:

FENa = (40 ÷ 14,000) × 100

FENa = 0.2857%

So, the fractional excretion of sodium is 0.29%.

Final Verdict

The fractional excretion of sodium calculator makes FENa math quick and simple. Enter four lab values, click calculate, and get the result.

A FENa below 1% may fit a prerenal pattern in the right setting. But this is not a diagnosis. Diuretic use and some kidney conditions can change FENa. So, the result should be read with the full clinical picture.

FAQs

What is a fractional excretion of sodium calculator?

It is an online tool that calculates FENa from urine sodium, serum sodium, urine creatinine, and serum creatinine.

What is the FENa formula?

FENa (%) = (Urine Sodium × Serum Creatinine) ÷ (Serum Sodium × Urine Creatinine) × 100.

What does a FENa below 1% mean?

A value below 1% may support a prerenal pattern in the right clinical setting. It does not prove the cause of kidney injury.

Do I need urine volume for FENa?

No. The standard spot-sample formula does not need urine volume.

Why does FENa use creatinine?

Creatinine helps adjust the sodium values for kidney filtration. This makes the calculation a fraction of filtered sodium that is excreted.

Can medicines affect FENa?

Yes. Diuretics can make FENa harder to interpret. Other kidney conditions can also change the result.