The Fractional Excretion of Uric Acid (FEUA) measures the percentage of filtered uric acid excreted in urine, helping differentiate between:
- Overproduction (e.g., tumor lysis)
- Underexcretion (e.g., chronic kidney disease)
- Tubular defects (e.g., Fanconi syndrome)
Key Formulas:
1. Standard FEUA Formula
FEUA (%) =
Urine Uric Acid × Serum Creatinine
Serum Uric Acid × Urine Creatinine
× 100
2. Unit-Specific Variations
- For mg/dL:
FEUA =
UUA (mg/dL) × SCr (mg/dL)
SUA (mg/dL) × UCr (mg/dL)
× 100
- For μmol/L:
FEUA =
UUA (μmol/L) × SCr (μmol/L)
SUA (μmol/L) × UCr (μmol/L)
× 100
🧲 Fractional Excretion of Uric Acid (FEUA) Calculator
📐 Formula:
FEUA (%) =
Urine Uric Acid × Serum Creatinine
Serum Uric Acid × Urine Creatinine
× 100
⚖️ Conversion Factors:
- Uric Acid: 1 mg/dL = 0.0595 mmol/L = 59.48 µmol/L
- Creatinine: 1 mg/dL = 0.0884 mmol/L = 88.42 µmol/L
Note: All values are internally converted to mg/dL for calculation consistency.
💊 Enter the Values:
Conversion Factors:
🧪 Uric Acid Conversion Factors
🔸 Urine Uric Acid & Serum Uric Acid
- mg/dL → mmol/L: mmol/L = mg/dL × 0.0595
- mmol/L → mg/dL: mg/dL = mmol/L ÷ 0.0595 or mmol/L × 16.8
🧪 Creatinine Conversion Factors
🔸 Urine Creatinine & Serum Creatinine
- mg/dL → mmol/L: mmol/L = mg/dL × 0.0884
- mmol/L → mg/dL: mg/dL = mmol/L ÷ 0.0884 or mmol/L × 11.31
Normal Values
- Normal FEUA: 4–11%
- <4%: Uric acid underexcretion (e.g., CKD, lead nephropathy)
- >11%: Uric acid overexcretion (e.g., tumor lysis, Fanconi syndrome)
Step-by-Step Calculation
Example (mg/dL Units)
- Urine Uric Acid (UUA): 50 mg/dL
- Serum Uric Acid (SUA): 6 mg/dL
- Urine Creatinine (UCr): 150 mg/dL
- Serum Creatinine (SCr): 1.2 mg/dL
FEUA =
50 × 1.2
6 × 150
× 100 =
60
900
× 100 = 6.67%
• Input values: UUA=50 μmol/L, SCr=1.2 mg/dL, SUA=6 μmol/L, UCr=150 μmol/L
• Normal range: 7-20% (this result suggests renal underexcretion)
Clinical Applications
1. Gout Management
- Low FEUA (<4%): Underexcretion → Consider uricosurics (probenecid)
- High FEUA (>11%): Overproduction → Consider xanthine oxidase inhibitors (allopurinol)
2. Tumor Lysis Syndrome
- FEUA >15% suggests massive uric acid release
3. Renal Disorders
- Fanconi Syndrome: FEUA >20% (proximal tubular dysfunction)
- AKI/CKD: FEUA <4% (reduced excretion)
Limitations
- Affected by diuretics, hydration status
- Requires simultaneous serum/urine samples
- Does not distinguish between glomerular/tubular causes
Key Takeaways
- Normal FEUA: 4–11%
- Low FEUA: Underexcretion (CKD, metabolic syndrome)
- High FEUA: Overproduction (tumor lysis) or tubular defects
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