FeUrea Calculator

FeUrea Calculator for Nephrology. Results are labeled below 35% or at/above 35% without decimal gaps. Published equality conventions vary; this numerical split is transparent and does not diagnose an etiology.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

FEUrea = 100 x (urine urea / blood urea) x (serum creatinine / urine creatinine), using matched concentration units for each pair. In US mode both urea inputs must be urea nitrogen in mg/dL, not one urea mass and one nitrogen concentration.

When to use this calculator

An adjunctive urine/serum clearance fraction in an appropriately timed clinical assessment.

Inputs used

  • Blood urea (SI) / BUN (US) (mmol/L; US mg/dL)
  • Urine urea (SI) / urine urea nitrogen (US) (mmol/L; US mg/dL)
  • Serum creatinine (umol/L; US mg/dL)
  • Urine creatinine (umol/L; US mg/dL)

Clinical interpretation

Results are labeled below 35% or at/above 35% without decimal gaps. Published equality conventions vary; this numerical split is transparent and does not diagnose an etiology.

Worked example

Urine urea 250, blood urea 40, serum creatinine 2 and urine creatinine 40 in matched pairs give 31.25%. Raising urine urea to 280 gives exactly 35%, labeled at the numerical threshold rather than assigned a renal diagnosis.

Limitations and safety notes

Loop diuretics can change FEUrea and reclassify patients around a cutoff. Low or high fractions do not establish prerenal AKI, ATN or fluid responsiveness; specimen timing and paired-analyte consistency remain essential.

Frequently asked questions

Is FEUrea unaffected by loop diuretics?

No. Primary prospective observations show meaningful changes after loop diuresis, so it is not a diuretic-proof discriminator.

What does this result leave unresolved?

Loop diuretics can change FEUrea and reclassify patients around a cutoff. Low or high fractions do not establish prerenal AKI, ATN or fluid responsiveness; specimen timing and paired-analyte consistency remain essential.

References

  • https://pubmed.ncbi.nlm.nih.gov/12427149/
  • https://pmc.ncbi.nlm.nih.gov/articles/PMC7798124/

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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