FEUrea Calculator: Acute Kidney Injury Cause Differentiation

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Conventional uses mg/dL for urea/BUN and creatinine. SI uses mmol/L for urea and umol/L for creatinine.
Blood urea nitrogen (BUN) in mg/dL or serum urea in mmol/L. Normal BUN: 8-20 mg/dL (2.9-7.1 mmol/L).
mg/dL
Serum creatinine in mg/dL or umol/L. Normal: 0.7-1.3 mg/dL (62-115 umol/L) for adults.
mg/dL
Spot urine urea concentration. Normal random urine urea: 200-400 mg/dL (70-140 mmol/L) but varies widely.
mg/dL
Spot urine creatinine concentration. Normal: 20-300 mg/dL. Low values suggest dilute urine or impaired tubular secretion.
mg/dL
FEUrea is preferred over FENa when the patient is receiving diuretics, which invalidate FENa but not FEUrea.
FEUreaPrerenal
20.1%

Fractional excretion of urea

InterpretationPrerenal azotemia likely
Confidence noteResult below 35% is consistent with prerenal azotemia. Correlate with clinical findings.
20.1% %
Strongly Prerenal<20Prerenal20-35Indeterminate35-50Intrinsic Renal50+

FEUrea 20.1%: prerenal pattern.

  • The kidneys are avidly reabsorbing urea along with water, a pattern seen in volume depletion and reduced renal perfusion.
  • Prerenal AKI typically responds to cautious fluid resuscitation; monitor creatinine and urine output closely.
  • FEUrea is a screening tool - results must always be interpreted alongside history, physical examination, imaging, and urine microscopy.

Next stepConsider a careful fluid challenge under monitoring, and repeat creatinine after resuscitation to confirm prerenal responsiveness.

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