📋 Clinical Utility: FEPO4 helps differentiate causes of phosphate wasting and evaluate phosphate handling in CKD.
Normal Range: 5-20% (varies with dietary phosphate intake)
Key Uses: Hypophosphatemia workup, CKD-MBD assessment, tumor-induced osteomalacia

👤 Patient Information (Optional)

Age

years

Sex

🧪 Serum Values *

Serum Phosphate (PO4) *

mg/dL

Normal range: 2.5-4.5 mg/dL (adults).

Serum Creatinine *

mg/dL

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

💧 Urine Values *

Urine Phosphate (PO4) *

mg/dL

Spot urine phosphate concentration.

Urine Creatinine *

mg/dL

Spot urine creatinine concentration.

🩺 Clinical Context (Optional)

CKD (eGFR < 60) Hypophosphatemia Suspected TIO Abnormal Calcium Phosphate Binders Vitamin D Deficiency

These contextual factors can affect FEPO4 interpretation.

📊 FEPO4 vs Other Fractional Excretion Tests

Feature	FEPO4	FENa	FEUrea
Marker	Phosphate	Sodium	Urea
Formula	(U_PO4/P_PO4) / (U_Cr/P_Cr) × 100%	(U_Na/P_Na) / (U_Cr/P_Cr) × 100%	(U_Urea/P_Urea) / (U_Cr/P_Cr) × 100%
Normal Range	5-20%	< 1% (prerenal)	< 35% (prerenal)
Primary Use	Phosphate wasting, CKD-MBD	Prerenal vs ATN	Prerenal vs ATN (diuretics)
Affected By	PTH, vitamin D, diet, CKD	Diuretics, CKD	Diet, GI bleeding
Clinical Pearl	> 20% suggests phosphate wasting	< 1% suggests prerenal	< 35% suggests prerenal

💡 Clinical Pearl: FEPO4 is essential for evaluating hypophosphatemia. In CKD, FEPO4 may be elevated despite normal phosphate due to secondary hyperparathyroidism.

📖 FEPO4 Formula:
FEPO4 = (Urine PO4 / Serum PO4) / (Urine Cr / Serum Cr) × 100%
Interpretation:
• 5-20%: Normal phosphate handling
• > 20%: Phosphate wasting (hyperparathyroidism, TIO, Fanconi syndrome)
• < 5%: Reduced phosphate excretion (hypoparathyroidism, phosphate retention)
Note: FEPO4 varies with dietary phosphate intake. A 24-hour urine collection may be needed for accurate assessment.

🧪 Fractional Excretion of Phosphate (FEPO4)

📊 FEPO4 Results

📊 FEPO4 vs Other Fractional Excretion Tests