Skip to content
Hakeemly
ع

Fractional Excretion of Urea (FEUrea)

Fractional excretion of urea, an alternative to FENa studied in AKI, including in patients who have received diuretics.

For healthcare professionalsKidneyv1.1.0

For healthcare professionals / clinical use. Not a self-diagnosis tool.

Your measurements

mg/dL (BUN)
mg/dL
mg/dL

Calculated on your device. Nothing is sent to a server.

Your result will appear here

Enter your measurements, then press Calculate.

Methodology

FEUrea (Carvounis 2002)

FEUrea = (UUrea × PCr) ÷ (PUrea × UCr) × 100

Carvounis (2002) proposed FEUrea because urea excretion is less influenced by diuretics; later meta-analyses found moderate accuracy, and in 2024 it was not a better alternative to FENa, even with diuretics.

Who it is for
Adults with acute kidney injury.
Version
1.1.0

How this calculator works

Where the formula comes from

  • Carvounis and colleagues (2002) prospectively compared the fractional excretion of urea nitrogen with FENa in 102 episodes of acute renal failure: 50 prerenal, 27 prerenal on diuretics and 25 acute tubular necrosis.[1]
  • Mean FEUrea was 27.9% and 24.5% in the two prerenal groups and 58.6% in acute tubular necrosis; 89% of diuretic-treated prerenal patients had FEUrea of 35% or less, while only 48% had FENa below 1%.[1]

The inputs

  • FEUrea (%) = (urine urea nitrogen × plasma creatinine) ÷ (plasma urea nitrogen × urine creatinine) × 100. In Carvounis and colleagues (2002), FEUrea of 35% or less was associated with prerenal azotaemia.[1]

Versions and alternatives

  • A 2024 meta-analysis (11 studies, 1,108 patients) found FEUrea above 35% had pooled sensitivity 66% and specificity 75% for intrinsic AKI and was not a better alternative to FENa, even with diuretics.[2]
  • A 2026 meta-analysis (12 studies, 1,240 patients) reported pooled sensitivity 0.74 and specificity 0.78, with very high heterogeneity and low certainty of evidence.[3]

Where accuracy falls (published evidence)

  • In 203 critically ill patients, FEUrea was of little help in separating transient from persistent AKI (AUC 0.59; at 35%, sensitivity 63% and specificity 54%), including in those on diuretics.[4]

Sources

  1. Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002;62(6):2223–2229. doi:10.1046/j.1523-1755.2002.00683.x
  2. Abdelhafez MO, Alhroob AA, Abu Hawilla MO, et al. Utility of fractional excretion of urea in acute kidney injury with comparison to fractional excretion of sodium: a systematic review and meta-analysis. Am J Med Sci. 2024;368(3):224–234. doi:10.1016/j.amjms.2024.04.021
  3. Pan HC, Jiang ZH, Chen HY, et al. Assessing the utility of fractional excretion of urea in distinguishing intrinsic and prerenal acute kidney injury in hospitalised patients: a systematic review and meta-analysis. BMJ Open. 2026;16(1):e100875. doi:10.1136/bmjopen-2025-100875
  4. Darmon M, Vincent F, Dellamonica J, et al. Diagnostic performance of fractional excretion of urea in the evaluation of critically ill patients with acute kidney injury: a multicenter cohort study. Crit Care. 2011;15(4):R178. doi:10.1186/cc10327

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on

Worked example: how to calculate FEUrea

Inputs

Plasma urea nitrogen
40 mg/dL (BUN)
Urine urea nitrogen
400 mg/dL
Plasma creatinine
2 mg/dL
Urine creatinine
100 mg/dL

Result

FEUrea
20 %

35% or less: pattern associated with prerenal states

Calculation:

400×2/(40×100)×100 = 20

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

  • In critically ill patients it was of little help in separating transient from persistent kidney injury, including with diuretics (2011 study).

References

  1. Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002;62(6):2223–2229. doi:10.1046/j.1523-1755.2002.00683.x
  2. Abdelhafez MO, Alhroob AA, Abu Hawilla MO, et al. Utility of fractional excretion of urea in acute kidney injury with comparison to fractional excretion of sodium: a systematic review and meta-analysis. Am J Med Sci. 2024;368(3):224–234. doi:10.1016/j.amjms.2024.04.021
  3. Darmon M, Vincent F, Dellamonica J, et al. Diagnostic performance of fractional excretion of urea in the evaluation of critically ill patients with acute kidney injury: a multicenter cohort study. Crit Care. 2011;15(4):R178. doi:10.1186/cc10327

You may also find useful