How this calculator works
Match the serum and urine reporting convention: either both urea nitrogen or both urea. The conversion cancels within their ratio. Use contemporaneous samples. The original study examined FEUrea in acute renal failure, including people receiving diuretics. FEUrea still has important limitations and cannot independently classify acute kidney injury. The result is an estimate for information only and is not medical advice.
Formula
FEUrea (%) = 100 × (urine urea × serum creatinine) / (serum urea × urine creatinine). Using urea nitrogen in both urea positions gives the same fractional result.
Worked example
Urine BUN 400, serum BUN 40, serum creatinine 2 and urine creatinine 100 mg/dL give 20%. Changing urine BUN to 800 mg/dL gives 40%.
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Frequently asked questions
Can I enter urine urea with serum BUN?
Only after converting one to the same reporting convention. This form applies a shared convention to both fields.
Is FEUrea unaffected by diuretics?
No. It may be less directly affected than FENa in some settings, but is not immune to clinical confounders.
What does 35% mean?
It was a study threshold, not a universal diagnostic boundary. The calculator reports the number without assigning a cause or treatment.