Fractional Excretion of Urea (FeUrea)

Calculates FeUrea, sometimes used as an adjunct when diuretics limit FeNa interpretation; FeUrea is also context-dependent and does not reliably distinguish prerenal physiology from intrinsic AKI by itself.

Formula

FeUrea = (Urine urea nitrogen × Plasma Cr) / (Plasma urea nitrogen × Urine Cr) × 100

Urine urea nitrogen (mg/dL)Plasma creatinine (mg/dL)Plasma urea nitrogen (BUN) (mg/dL)Urine creatinine (mg/dL)

Result

Enter all values to see the result.

Limitations

FeUrea is not a validated 'fix' for FeNa after diuretics; its diagnostic performance is also imperfect in sepsis, CKD and mixed ICU physiology.
Urea handling can also be affected by protein intake, catabolic state, and liver function, which can shift the result independent of the prerenal/intrinsic distinction.
A single value is a probabilistic aid, not a definitive diagnostic test — it should be interpreted alongside the full clinical picture, not in isolation.

References

Carvounis CP, et al. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002.

Clinical Context & Relevant Topics (2)

Disease Reference

Acute Kidney Injury in Critical Care

Sepsis-AKI microcirculatory decoupling, KDIGO staging, Furosemide Stress Test (FST), urine microscopy, and the AEIOU dialysis threshold framework.

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Continuous Renal Replacement Therapy (CRRT)

Principles of convection vs diffusion, filtration fraction, delivered effluent dosing (20–25 mL/kg/h), Regional Citrate Anticoagulation, and citrate toxicity.

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Relevant Clinical Pathways (8)

Decision Protocols

Renal Replacement Therapy & CRRT Initiation

From urgent 'AEIOU' indication screening and modality selection to vascular access, dosing, and anticoagulation.

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Severe Hyperkalemia Emergency Management

From emergent cardiac membrane stabilization to intracellular shifting, elimination, and dialysis triggers.

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