FEUrea Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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In nephrology and urology, the same number can mean different things in acute illness, chronic disease, or imaging follow-up. FEUrea Calculator handles the arithmetic while the clinical setting supplies the meaning.

What this calculator does

FEUrea Calculator uses Serum creatinine, Serum urea / BUN, Urine creatinine, and Urine urea / BUN to calculate fractional excretion of urea. It is built around the exact fields displayed in this plugin rather than a generic version of the topic. Kidney calculations often depend on paired laboratory samples, stable physiology, and the population in which the equation was validated. Acute changes in kidney function or nonstandard sampling can make an apparently precise number unreliable.

How to use it

Enter or select Serum creatinine, Serum urea / BUN, Urine creatinine, and Urine urea / BUN. Use the units offered by the calculator and choose the option that matches the actual clinical or timing situation. Check date entries and laboratory units before relying on the output. For paired blood, urine, or dialysis measurements, use samples and treatment data from the same collection or clinical episode when the formula requires it.

How the calculation works

Fractional excretion of urea is calculated as (urine urea or BUN × serum creatinine) / (serum urea or BUN × urine creatinine) × 100. The output is a percentage based on paired serum and urine measurements.

Example

Using the sample values prefilled in this calculator, the primary result is 10 % (Fractional excretion of urea). This worked example shows how the plugin’s own default inputs flow through the implemented method; replace them with the correct patient, laboratory, imaging, or personal values before interpreting a result.

How to interpret the result

Interpret the output as fractional excretion of urea from the formula implemented here. Compare it with the relevant laboratory, imaging, pathology, or treatment context, and use trends or a validated clinical pathway when appropriate. One calculated value by itself cannot establish the cause of a urologic or kidney problem or predict an individual outcome.

Limitations and notes

FEUrea is sometimes used when diuretics make FENa harder to interpret, but it is not immune to confounding and evidence for fixed diagnostic cutoffs is imperfect. Sepsis, CKD, catabolism, and timing of samples can affect the result.