FENa Calculator

FENa Calculator: Easily Determine Sodium Levels

When it comes to understanding your kidney health, one tool that has taken the medical world by storm is the FENa Calculator.

This inventive tool offers a simple yet strong method for assessing your kidney function and detecting potential issues from the beginning.

The Fractional Excretion of Sodium (FENa) is an important clinical indicator that assists in determining the levels of sodium in the body. This calculation is particularly relevant in the diagnosis and management of various renal and non-renal conditions.

In this article, we dive into the meaning of the FENa Calculator and how it can give significant bits of knowledge to your general prosperity.

What is Fena?

FENa, or fractional excretion of sodium, is a clinical parameter used to assess the percentage of filtered sodium that is excreted in the urine. It is commonly employed in the evaluation of acute kidney injury to help differentiate between prerenal and intrinsic renal causes.

How to calculate your FENa (Fractional Excretion of Sodium)?

To calculate your FENa (Fractional Excretion of Sodium), you will need to perform FENa test in a laboratory.


This is a measure of kidney function and is typically reported in mg/dL. Normal levels of creatinine in blood are approximately 0.6 to 1.2 mg/dL in adult males and 0.5 to 1.1 mg/dL in adult females.

Sodium (Na+)

The serum sodium test provides the level of sodium in your blood.

Urine Creatinine

The doctor may use a casual urine sample or a urine 24-hour volume test to measure creatinine in urine. This test helps in assessing kidney function by looking at the amount of creatinine excreted in the urine over a specific period.

Urine Sodium

This test measures the amount of sodium in all urine collected during 24 hours. The reference range for urine sodium is typically 100-260 mmol/L per 24 hours.

Fena Formula



  • UNa is the urinary sodium concentration.
  • PCR is the plasma creatinine concentration.
  • PNa is the plasma sodium concentration.
  • UCr is the urinary creatinine concentration.

Example of calculating the FENa.

Suppose you have the following laboratory values for a patient:

  • UNa (urinary sodium concentration): 40 mEq/L
  • PCR (plasma creatinine concentration): 1.2 mg/dL
  • PNa (plasma sodium concentration): 140 mEq/L
  • UCr (urinary creatinine concentration): 80 mg/dL

Now, you can use the FENa formula


FENa=40mEq/L×1.2mg/dL/140mEq/L​×80 mg/dL​×100

Calculate the numerator and denominator:


Now, perform the division:


So, FENa≈42.86%

In this example, the calculated FENa is approximately 42.86%. The explanation would depend on the clinical context and the specific ranges associated with different kidney conditions.

This formula helps determine the percentage of filtered sodium that is excreted in the urine. The interpretation you provided is also accurate in terms of clinical conditions associated with different FENa values.

FENa greater than 1% and usually greater than 3% with acute tubular necrosis and severe obstruction of the urinary drainage of both kidneys.

FENa is generally less than 1% in patients with acute glomerulonephritis, hepatorenal syndrome, and states of prerenal azotemia such as congestive heart failure or dehydration.
FENa may also be less than 1% with acute partial urinary tract obstruction.

As mentioned earlier, a FENa greater than 1% and usually greater than 3% may suggest certain conditions like acute tubular necrosis. Always consult with healthcare professionals for proper interpretation and clinical decision-making.

What is the FENa Calculator?

The FENa (Fractional Excretion of Sodium) Calculator is a helpful tool that figures out a number to tell us about our kidneys. It uses results from blood and pee tests (like sodium and creatinine levels) to calculate this number.

To calculate FENa using the provided FENa Calculator,

Just Enter the Values in Our FENa Calculator

Enter the urine sodium level (in mEq/L) in the “Urine Sodium level” field.
Enter the plasma sodium level (in mEq/L) in the “Plasma Sodium level” field.
Enter the urine creatinine level (in mg/dL) in the “Urine Creatinine level” field.
Enter the plasma creatinine level (in mg/dL) in the “Plasma Creatinine level” field.

Click the “Calculate FENa” button.

The calculator will use these values in the FENa formula, and the result, representing the Fractional Excretion of Sodium, will be displayed in the “FENa (Fractional Excretion of Sodium)” field. This calculated value helps assess kidney function, with higher or lower FENa values potentially indicating different kidney conditions.

Why FENa Matters: The Importance of FENa in Kidney Health

Knowing your FENa value can be crucial in identifying kidney issues early on.

  • A high FENa value could indicate acute kidney injury.
  • A low value might suggest prerenal conditions like dehydration.

Understanding your FENa value is important for catching kidney problems early. A high FENa might mean kidney injury, while a low value could signal issues like dehydration.

Checking your FENa regularly helps your healthcare provider make smart decisions about your kidney health and treatment. It’s a simple way to stay on top of your well-being and address any kidney concerns early.


What is the FENa Calculator?

The FENa Calculator is a tool used to calculate the Fractional Excretion of Sodium (FENa), a measure that helps assess kidney function. It requires input values such as urine and plasma sodium and creatinine levels.

Why is FENa important?

FENa is crucial in evaluating kidney health. It can indicate conditions such as acute kidney injury or dehydration. Monitoring FENa helps in early detection and timely management of kidney issues.

What do I need to use the FENa Calculator?

You need results from specific tests: urine sodium, plasma sodium, urine creatinine, and plasma creatinine levels. Enter these values into the calculator to get your FENa result.

What does a high or low FENa value mean?

A high FENa might suggest kidney injury, while a low value could indicate conditions like dehydration. The interpretation depends on clinical context and should be discussed with a healthcare professional.

How often should I use the FENa Calculator?

The frequency depends on your health condition and your healthcare provider’s recommendations. It might be used during regular check-ups or if there are concerns about kidney function.

Can I rely solely on the FENa Calculator for kidney health assessment?

The FENa Calculator is a helpful tool, but it should be used in conjunction with other clinical and laboratory findings. Consult with a healthcare professional for a comprehensive evaluation of kidney health.

Is the FENa Calculator suitable for self-diagnosis?

No, the FENa Calculator is not a substitute for professional medical advice. It is a tool for informational purposes, and any concerns about kidney health should be discussed with a qualified healthcare provider.

Can the FENa Calculator be used for pediatric patients?

The calculator is primarily designed for adult populations. Pediatric cases may require different reference ranges, and it’s essential to consult with a healthcare professional for accurate assessment of children.

Is the FENa Calculator suitable for individuals with chronic kidney disease (CKD)?

The FENa Calculator can be used in various kidney conditions, but its interpretation may vary. Individuals with CKD should follow their healthcare provider’s guidance for a more comprehensive evaluation of kidney function.


It’s really important to find out about kidney problems early to stay healthy. The FENa Calculator is a helpful tool for people and doctors. It helps catch kidney issues early before they become big problems.

Checking regularly with the FENa Calculator is a smart way to take care of your kidneys and avoid serious damage in the long run. It’s all about keeping an eye on your health and acting quickly if there’s a concern.

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