FENa Calculator
Calculate Fractional Excretion of Sodium to differentiate causes of acute kidney injury
Calculate FENa
Normal: 0.6-1.2 mg/dL (men), 0.5-1.1 mg/dL (women)
Normal: 135-145 mmol/L
Varies widely; typically 20-370 mg/dL
Normal: 100-260 mmol/L per 24 hours
FENa Reference Ranges
Prerenal
Decreased renal perfusion
Intrinsic
Intrinsic kidney damage
Postrenal
Urinary tract obstruction
Required Lab Tests
Blood Tests
Serum creatinine and sodium
Urine Tests
Urine creatinine and sodium
Random or 24-hour collection
When to Use FENa
Acute kidney injury evaluation
Oliguria or anuria workup
Differentiating AKI causes
Patients on diuretics
Chronic kidney disease
Example Calculation
Sample Values
Plasma Cr: 2.0 mg/dL
Plasma Na: 140 mmol/L
Urine Cr: 80 mg/dL
Urine Na: 15 mmol/L
Calculation
FENa = (2.0 × 15) / (140 × 80) × 100
FENa = 30 / 11,200 × 100
FENa = 0.27%
Result: Prerenal cause
Understanding FENa (Fractional Excretion of Sodium)
What is FENa?
FENa represents the percentage of filtered sodium that is excreted in the urine. It's a valuable tool for differentiating the causes of acute kidney injury by assessing how well the kidneys are conserving sodium in response to decreased perfusion or intrinsic damage.
Clinical Significance
- •Helps distinguish prerenal from intrinsic AKI
- •Guides appropriate treatment strategies
- •Assists in prognosis assessment
- •Valuable in critical care settings
Formula Explanation
FENa = (PCr × UNa) / (PNa × UCr) × 100
- PCr: Plasma creatinine concentration
- UNa: Urine sodium concentration
- PNa: Plasma sodium concentration
- UCr: Urine creatinine concentration
Physiological Basis: In prerenal AKI, the kidneys retain their ability to conserve sodium, resulting in low FENa. In intrinsic AKI, this ability is impaired, leading to higher FENa values.
⚠️ Important Medical Disclaimer
This calculator is for educational purposes only and should not replace professional medical advice.
- • Always consult with a qualified nephrologist or physician for AKI evaluation
- • FENa should be interpreted within the full clinical context
- • Consider other diagnostic tests and clinical findings
- • Monitor patient closely and adjust treatment based on response
- • Be aware of the limitations of FENa in certain clinical scenarios