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Fractional Urea Excretion from Paired Samples

Use paired urine and serum measurements.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Health results are educational estimates, not a diagnosis or treatment recommendation. A qualified clinician can interpret measurements in the context of your health.

Formula and method

Paired values 800, 1, 40 and 100 in matching mass concentration units give 20%.

FEurea (%) = 100 × urine urea × serum creatinine / (serum urea × urine creatinine).

Worked example

Enter these known values and leave the other values blank.

Serum creatinine
1 mg/dL
Serum urea
40 mg/dL
Urine creatinine
100 mg/dL
Urine urea
800 mg/dL
Feurea
20 %

Assumptions and limitations

  • Use paired urine and serum measurements. Match urea units to urea, and creatinine units to creatinine; do not mix urea with urea nitrogen. The 2002 study evaluated acute renal failure cohorts; its threshold is not a standalone diagnostic rule. Molar conversion uses 60.06 g/mol for urea. BUN mass values must be converted before entering the urea controls.
  • Arithmetic inverses use independent observations. Clear the unknown control before entering the remaining measurements.
  • This measurement calculation does not determine a diagnosis or treatment.

Common questions

How is this result calculated?

FEurea (%) = 100 × urine urea × serum creatinine / (serum urea × urine creatinine).

Which measurements and units should I use?

Use paired urine and serum measurements. Match urea units to urea, and creatinine units to creatinine; do not mix urea with urea nitrogen. The 2002 study evaluated acute renal failure cohorts; its threshold is not a standalone diagnostic rule.

References

Bookify adds independently reviewed bounds for feurea: serum_creatinine > 0; serum_urea > 0; urine_creatinine > 0; urine_urea >= 0. Urea molar selectors use the stated 60.06 g/mol convention (6.006 mg/dL per mmol/L), replacing the captured urea-nitrogen conversion.

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