Fractional Excretion of Urea (FEUrea)

What This Calculator Measures

Estimates the fractional excretion of urea to help distinguish prerenal azotemia from intrinsic renal injury, particularly useful when diuretics make FENa unreliable.

How to Use

1. Use when the patient is receiving diuretics or FENa is otherwise unreliable.
2. Obtain paired urine urea, plasma urea, urine creatinine, and plasma creatinine.
3. Enter all four values.
4. Review the FEUrea and its suggested category.

Interpretation Guide

FEUrea < 35% suggests prerenal azotemia, 35–50% is indeterminate, and > 50% suggests intrinsic renal injury such as ATN. Because urea reabsorption is less affected by diuretics than sodium, FEUrea retains diagnostic utility in patients on diuretics.

Clinical Significance

Because diuretics blunt the diagnostic utility of FENa, FEUrea provides a useful complementary test for the prerenal-versus-intrinsic distinction in patients on diuretics.

When to Use

• AKI evaluation when diuretics have been given
• Complementing FENa in the prerenal-versus-intrinsic distinction
• When the BUN/Cr ratio is inconclusive

When Not to Use

• As a replacement for FENa when no diuretics are involved
• As a standalone diagnostic test
• In severe liver disease, where urea production is reduced

Limitations

• Less widely validated than FENa.
• Urea handling is influenced by protein intake, catabolic states, and corticosteroids.
• Reduced hepatic urea production affects both serum and urine urea.
• Thresholds are less well established in some populations.

Worked Example

A 68-year-old woman with heart failure on furosemide has a urine urea of 300 mg/dL, plasma urea 25 mg/dL, urine creatinine 100 mg/dL, and plasma creatinine 1.5 mg/dL.

FEUrea = (300/25) ÷ (100/1.5) × 100 ≈ 18%. This value below 35% suggests prerenal azotemia.

Evidence

Source

Nephrology

Reference

Pépin MN, et al. Reassessment of the fractional excretion of urea for the differential diagnosis of acute renal failure. Clin Invest Med. 2007;30(5):E163-167.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

1. Pépin MN, et al. Clin Invest Med. 2007;30(5):E163-167.

References

1. Pépin MN, et al. Reassessment of the fractional excretion of urea for the differential diagnosis of acute renal failure. Clin Invest Med. 2007;30(5):E163-167. (Validation Study)

Frequently Asked Questions