FEUrea Calculator

What Is FEUrea?

Fractional excretion of urea (FEUrea) measures how much filtered urea is lost in urine relative to creatinine handling. It helps distinguish prerenal azotemia from intrinsic renal injury, especially when diuretics make FENa unreliable. Pair results with the FENa Calculator and BUN to Creatinine Ratio Calculator.

FEUrea Formula

$$FEUrea = \frac{U_{urea} \times P_{Cr}}{U_{Cr} \times P_{urea}} \times 100\%$$

Collect simultaneous urine and blood samples. Urea and creatinine must use consistent units before calculation.

Clinical Interpretation

FEUrea below 35%: suggests prerenal azotemia (appropriate renal urea retention)
FEUrea 35–50%: indeterminate; correlate with volume status and other labs
FEUrea above 50%: suggests intrinsic renal disease such as acute tubular necrosis

When FEUrea Is Preferred Over FENa

FEUrea is particularly useful in patients receiving loop or thiazide diuretics, where sodium excretion rises independently of perfusion. It is still only one data point and must be interpreted in clinical context.

Frequently Asked Questions

What is the FEUrea formula?

FEUrea (%) = (urine urea × plasma creatinine) / (urine creatinine × plasma urea) × 100. All creatinine values must share the same unit, and urea values must share the same unit.

What does FEUrea below 35% mean?

It suggests prerenal azotemia: kidneys retain urea when perfusion is low. Common causes include hypovolemia, heart failure, and hepatorenal syndrome.

What does FEUrea above 50% indicate?

It suggests intrinsic renal injury with impaired tubular reabsorption, such as acute tubular necrosis or acute interstitial nephritis.

Does this calculator support SI units?

Yes. Select mg/dL or mmol/L for urea and mg/dL or μmol/L for creatinine. The calculator converts internally before applying the formula.

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