Fractional Excretion of Sodium Test
Short Name: FENa Test
Also known as: FENa Test, Fractional Excretion of Sodium, Sodium Fractional Excretion, FENa Fraction Test, Urine Sodium Fraction Test
Fractional Excretion of Sodium Test test available at DNA Labs India for ₹878. Uses Jaffe's Reaction (for Creatinine), Indirect Ion-Selective Electrode (ISE) (for Sodium) on Serum (from SST) and Random Urine samples. Results in Same day (daily reporting schedule). Results are typically available within a few hours of sample receipt at the laboratory.. Free home collection in 300+ cities across India.
🩺 Medically Reviewed By
Dr Ramarao Paidisetty
Consultant Biochemist · Reg: 21504
Last reviewed: September 7, 2026
Overview
The FENa test is performed to determine whether kidney dysfunction is caused by reduced blood flow to the kidneys (prerenal) or by damage within the kidney tissue itself (intrinsic renal). This distinction is critical for guiding treatment decisions. In prerenal conditions, restoring fluid volume may resolve the dysfunction, whereas intrinsic renal injury may require different interventions. The test is also used to evaluate the effectiveness of diuretic medications in conditions such as heart failure, hypertension, and fluid overload states.
- Test Code
- 622
- Price
- ₹878
- Sample Type
- Serum (from SST) and Random Urine
- Result Time
- Same day (daily reporting schedule). Results are typically available within a few hours of sample receipt at the laboratory.
- Fasting Required
- No
- Method
- Jaffe's Reaction (for Creatinine), Indirect Ion-Selective Electrode (ISE) (for Sodium)
Sample Collection
No special preparation or fasting is required. Inform your doctor about all medications you are currently taking, especially diuretics, as these may affect results. Stay normally hydrated before the test.
Method: Venipuncture for serum; clean-catch midstream urine collection
Laboratory Analysis
A blood sample (approximately 3 mL) will be drawn from a vein in your arm into a serum separator tube (SST). You will also be asked to provide a midstream random urine sample (approximately 10 mL minimum) in a sterile screw-capped container. The process typically takes 10–15 minutes.
Report Delivery
After blood collection, slight bruising or soreness at the venipuncture site may occur and usually resolves within a day. You may resume normal activities immediately. No dietary or activity restrictions apply after sample collection.
Timeline: Same day (daily reporting schedule). Results are typically available within a few hours of sample receipt at the laboratory.
Patient Instructions
About This Test
Who Should Get This Test
The FENa test is performed to determine whether kidney dysfunction is caused by reduced blood flow to the kidneys (prerenal) or by damage within the kidney tissue itself (intrinsic renal). This distinction is critical for guiding treatment decisions. In prerenal conditions, restoring fluid volume may resolve the dysfunction, whereas intrinsic renal injury may require different interventions. The test is also used to evaluate the effectiveness of diuretic medications in conditions such as heart failure, hypertension, and fluid overload states.
How to Prepare
- No fasting required; maintain normal hydration
- Provide a clean-catch midstream urine sample in the sterile container provided
- Blood sample will be collected via venipuncture into an SST tube
- Inform the phlebotomist about any diuretic or antihypertensive medication use
- Samples are shipped refrigerated or frozen to maintain stability
Doctor's Notes
Reviewed by Dr Ramarao Paidisetty — MBBS, MD (Biochemistry) · Reg. No. 21504
"The Fractional Excretion of Sodium is a critical bedside index that helps differentiate prerenal azotemia from intrinsic renal injury. A FENa value below 1% typically indicates intact tubular function with avid sodium reabsorption, commonly seen in prerenal states such as volume depletion or heart failure. A FENa above 1% suggests intrinsic tubular damage, as seen in ischemic or nephrotoxic acute kidney injury. However, clinicians should interpret FENa with caution — low values can also occur in glomerulonephritis and hepatorenal syndrome, and should never be used as the sole guide for volume management. FENa is most reliable when oliguria is present and when patients are not on diuretics."
Last medically reviewed: September 7, 2026
Test Parameters & Specifications
Sample Stability
- Urine sample not collected in a sterile screw-capped container
- Serum sample hemolyzed or insufficient volume (less than 2 mL)
- Urine volume less than 5 mL
- Sample received at room temperature beyond 6 hours of collection
- Mislabeled or unlabeled samples
Understanding Your Results
Suggests prerenal azotemia — the kidneys are reabsorbing sodium avidly due to reduced perfusion, volume depletion, or decreased effective circulating volume. Common in dehydration, heart failure, and hepatorenal syndrome. May also be seen in acute glomerulonephritis.
Status: Prerenal
Range: FENa < 1%
Suggests intrinsic renal injury, particularly acute tubular necrosis (ATN). The damaged tubules cannot reabsorb sodium effectively. Common in ischemic AKI and nephrotoxic kidney injury. The value may exceed 2–3% in established ATN.
Status: Intrinsic Renal
Range: FENa > 1%
Indeterminate range that requires clinical correlation. Consider repeating the test, evaluating FEUrea, and reviewing medication history (especially diuretic use). May represent transitional phase of kidney injury.
Status: Indeterminate
Range: FENa between 1–2%
Strongly suggests established acute tubular necrosis or significant tubular dysfunction. Often accompanied by muddy brown casts in urine sediment, elevated serum creatinine, and oliguria.
Status: Established ATN
Range: FENa > 3–4%
Consult a nephrologist or your treating physician if your FENa result is abnormal, if you have symptoms of kidney disease (such as reduced urine output, swelling in the legs or face, persistent fatigue, nausea, or shortness of breath), or if your serum creatinine or BUN levels are elevated. Early evaluation can help identify the cause and prevent progression of kidney damage.
Limitations
- ⚠FENa is most reliable in oliguric patients with established acute kidney injury
- ⚠Not recommended as the sole criterion for volume management decisions
- ⚠Should not be used interchangeably with Fractional Excretion of Urea (FEUrea) without clinical consideration
- ⚠Results may be unreliable in patients on diuretics — FEUrea may be preferred in such cases
- ⚠Low FENa does not always indicate intravascular volume depletion; conditions like glomerulonephritis and hepatorenal syndrome also present with low values
- ⚠Must be interpreted alongside clinical findings, urine output, serum electrolytes, and imaging studies
Risks & Considerations
- ●Minor bruising or discomfort at the blood draw site
- ●Very rare risk of infection at the venipuncture site
- ●No significant risks associated with urine collection
Interfering Factors
- ●Use of diuretics (e.g., furosemide, thiazides) can falsely elevate FENa
- ●Recent administration of mannitol or radiocontrast agents may affect results
- ●Patients with acute glomerulonephritis may show low FENa despite intrinsic renal disease
- ●Hepatorenal syndrome can produce low FENa values that mimic prerenal azotemia
- ●Non-oliguric acute kidney injury may yield unreliable FENa values
- ●Recent sodium intake or IV fluid administration can alter urinary sodium excretion
Compare With Similar Tests
| Test | Fractional Excretion of Sodium Test | Fractional Excretion of Urea (FEUrea) | Serum Creatinine | Blood Urea Nitrogen (BUN) / Creatinine Ratio | Urinalysis with Microscopy |
|---|---|---|---|---|---|
| Comparison | Fractional Excretion of Sodium Test | FEUrea is preferred over FENa in patients receiving diuretics, as diuretics increase urinary sodium excretion and can make FENa unreliable. FEUrea <35% suggests prerenal cause; >50% suggests intrinsic renal injury. | Serum creatinine reflects overall kidney filtration capacity but does not distinguish between prerenal and intrinsic renal causes. FENa provides tubular-level insight that serum creatinine alone cannot. | A BUN-to-creatinine ratio above 20:1 can suggest prerenal azotemia but is less specific than FENa. FENa directly measures sodium handling by the tubules and is a more specific discriminator. | Urinalysis can reveal casts (muddy brown casts in ATN), proteinuria, and hematuria. Combined with FENa, it provides a comprehensive assessment of the site and nature of kidney injury. |
Frequently Asked Questions
What is the Fractional Excretion of Sodium (FENa) test?
Why is the FENa test ordered?
What does a FENa value less than 1% indicate?
What does a FENa value greater than 1% indicate?
Do I need to fast before the FENa test?
What samples are required for the FENa test?
Can diuretics affect my FENa test results?
What is the cost of the FENa test at DNA Labs India?
Is home sample collection available for the FENa test?
How soon will I receive my FENa test results?
Is the FENa test used to monitor chronic kidney disease (CKD)?
What should I do if my FENa result is abnormal?
Related Tests
Reference Laboratory Services
We serve as a reference laboratory for hospitals and clinics across India. Send samples from your facility with same-day pickup, priority processing, and results delivered through our online portal. Competitive institutional pricing available.
Your Data Privacy
Your medical data is protected under Indian law.
✓ Stored in India: All patient records are stored on servers located in India. No data is transferred outside the country.
✓ DPDP Act Compliant: Under the Digital Personal Data Protection Act 2023, you can request deletion of your records at any time by contacting support.
Book Your Test
Enter your details and we'll connect you within 15 minutes.