FENa Calculator

FENa Calculator

Urine Sodium (UNa):
Urine Creatinine (UCr):
Plasma Sodium (PNa):
Plasma Creatinine (PCr):
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FENa Formula:

FENa = (UNa * PCr) / (UCr * PNa) * 100%

FENa Definition

For those familiar with chemistry, FENa is probably something that has been encountered previously, or at least heard of in passing. However, for those who may be scratching their heads and wondering what it is, FENa is an abbreviated way of indicating the fractional excretion of sodium, which in turn indicates the percentage of sodium in urine which has been filtered through the kidneys.

FENa is a very important medical benchmark, it is used to detect the risk and / or onset of acute renal failure and a handful of other serious conditions. Consequently, the calculations used in determining one’s fractional sodium excretion must be very precise. Readings are usually obtained through the use of complex formulas, but now, there exists an alternative to such laborious mathematical gymnastics – the FENa Calculator. You’ll find it below.

FENa Calculator

The FENA Calculator is quick and easy to use. Just enter the corresponding values the following inputs…

  • Urine Sodium (UNa) – This is the sodium content in a given urine sample which has been filtered by the kidneys.
  • Urine Creatinine (UCR) – This is the creatinine level in a given sample of urine which has been filtered by the kidneys.
  • Plasma Sodium (PNa) – This is the concentration of sodium in a blood sample, which is often used as an indication of hypertension and diabetes, in addition to its use in FENa calculation described here.
  • Plasma Creatinine (PCR) – This reading shows a blood sample’s level of creatinine.

…and the FENa Calculator will immediately calculate the remaining values, saving both the patient and their caregiver valuable time, as well as lowering the instances of human error which might otherwise be present.


At this point, it is worth noting that whatever readings you may obtain through your use of this FENa calculator, other data may also be necessary to obtain an accurate assessment of the situation. Additionally, while there is obviously a “normal” range for this type of test, readings can remain satisfactory in spite of their deviation from it, generally on the higher end. This is due to the fact that sodium and creatinine levels can present differently in very young children, especially neonates, as well as in those patients taking diuretics or other medication.

In the case of improper or failed readings after use of this or any other FENa calculation tool, it is important to remember that there are other ways of gathering the same information. Again, diuretics can unbalance FENa readings, so it may prove necessary to get a reading on the fractional excretion of other substances, such as uric acid or lithium.

In any case, consultation with a qualified, trusted medical professional to discuss independent readings obtained through the use of this calculator is highly recommended.

Be sure to check out some of the other Health Calculators we have here on CalculatorPro.com!

How to Calculate FENa

Let's be honest - sometimes the best fena calculator is the one that is easy to use and doesn't require us to even know what the fena formula is in the first place! But if you want to know the exact formula for calculating fena then please check out the "Formula" box above.

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