feurea calculator

What is FEUrea?

The Fractional Excretion of Urea (FEUrea) estimates the percentage of filtered urea that is excreted in urine. In acute kidney injury (AKI) workups, FEUrea can help distinguish likely prerenal physiology from intrinsic renal injury, especially when diuretics may make FENa less reliable.

Why clinicians use a FEUrea calculator

In a practical setting, FEUrea is often used as a quick bedside support metric. When blood flow to the kidneys is reduced (for example, dehydration, low effective circulating volume, or heart failure), the kidneys tend to reabsorb more urea. This typically leads to a lower FEUrea. In intrinsic tubular injury, urea handling is less efficient, and FEUrea tends to be higher.

• Lower FEUrea is more consistent with prerenal states.
• Higher FEUrea may suggest intrinsic renal injury (such as ATN), depending on context.
• Intermediate values require careful interpretation with full clinical data.

How to use this FEUrea calculator correctly

1) Use paired urine and plasma labs

The urine and plasma samples should be reasonably close in time so the ratio reflects the same physiologic state.

2) Keep unit consistency

Urea values should be in the same unit pair (urine/plasma), and creatinine values should also be matched. The formula is ratio-based, so consistency is essential.

3) Interpret trends, not just one number

FEUrea should not be used in isolation. Compare with volume status, blood pressure, urine sediment, medication profile, and serial labs.

Common interpretation ranges

• < 35%: Often supports prerenal physiology.
• 35% to 50%: Indeterminate zone; interpret with caution.
• > 50%: May be more consistent with intrinsic renal injury.

These cutoffs are rules of thumb and may vary by institution, patient population, and assay methods.

FEUrea vs FENa

FENa (Fractional Excretion of Sodium) is another common AKI index. However, sodium handling can be significantly altered by loop and thiazide diuretics. FEUrea is often preferred in those cases because urea handling may be less influenced by diuresis, though it is still not perfect.

Limitations and clinical caveats

• Recent diuretic exposure can still complicate interpretation.
• Sepsis, CKD, liver disease, and catabolic states may shift expected patterns.
• Early or mixed AKI etiologies can produce borderline or conflicting values.
• Single-point calculations are less useful than repeated measurements with clinical reassessment.

Bottom line

FEUrea is a useful adjunct for AKI evaluation and can be especially practical when diuretics blur sodium-based metrics. Use this calculator for quick estimation, but anchor decisions in the full clinical picture. Numbers inform care; context directs it.