📋 Clinical Utility: FEUrea < 35% suggests prerenal azotemia, while > 35% suggests ATN.
Advantage: Less affected by diuretics compared to FENa. Compare with FENa ↓

👤 Patient Information (Optional)

Age

years

Sex

🧪 Serum Values *

Serum Urea Nitrogen (BUN) *

mg/dL

Normal range: 7-20 mg/dL. Also known as BUN.

Serum Creatinine *

mg/dL

Normal range: 0.7-1.3 mg/dL (adults)

💧 Urine Values *

Urine Urea Nitrogen *

mg/dL

Spot urine urea nitrogen concentration.

Urine Creatinine *

mg/dL

Spot urine creatinine concentration.

🩺 Clinical Context (Optional)

Oliguria (UO < 400 mL/day) Recent Diuretics Sepsis/Hypotension Recent Nephrotoxins Pre-existing CKD Low Urine Flow State

These contextual factors can affect FEUrea interpretation.

📊 FENa vs FEUrea Comparison

Feature	FENa	FEUrea
Formula	(U_Na/P_Na) / (U_Cr/P_Cr) × 100%	(U_Urea/P_Urea) / (U_Cr/P_Cr) × 100%
Prerenal Cutoff	< 1%	< 35%
ATN Cutoff	> 2%	> 35%
Effect of Diuretics	Significantly increased (false ATN)	Minimally affected
Effect of CKD	May be elevated	May be elevated
Sensitivity	~90% for prerenal	~90% for prerenal
Specificity	~85% for ATN	~85% for ATN
Best Use	No diuretics, non-CKD	Diuretics, uncertain FENa

💡 Clinical Pearl: When FENa is borderline or unreliable due to diuretics, FEUrea < 35% strongly suggests prerenal azotemia. Consider using both tests together for improved diagnostic accuracy.

📖 FEUrea Formula:
FEUrea = (Urine Urea / Serum Urea) / (Urine Cr / Serum Cr) × 100%
Interpretation:
• < 35%: Prerenal azotemia
• > 35%: ATN (or other intrinsic renal injury)
Advantages over FENa: Less affected by diuretics, more stable in low urine flow states. Limitations: May be altered by high protein diet, GI bleeding, or steroid use.

🧪 Fractional Excretion of Urea (FEUrea)

📊 FEUrea Results

📊 FENa vs FEUrea Comparison