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FENa (Fractional Excretion of Sodium) Calculator
Calculate your fractional excretion of sodium (FENa%) easily. Accessible, accurate, and user-friendly tool for kidney function assessment using standard labs.
Not sure what your numbers are? Do a test here.
This calculator provides an estimate and should not replace medical advice.
Your fractional excretion of sodium (FENa) is in a range that may signal an imbalance in how your kidneys manage salt and water—an area to pay attention to and aim for steady improvement.
Your FENa% is in a generally healthy range—reflecting stable salt and fluid balance while leaving room to fine‑tune based on hydration, symptoms, and recent medications.
Your FENa% suggests strong, context-appropriate kidney sodium handling—great job; keep up the balanced routines that support steady hydration and overall stability.
Your fractional excretion of sodium (FENa) sits in the optimal range—indicating peak kidney sodium handling and strong long-term health potential.
What does your result mean?
This is your estimated fractional excretion of sodium (FENa%).
If you are:
- In range: 1–2% suggests an indeterminate zone where context matters. Keep usual routines, and interpret alongside your exam, urine output, and recent meds (especially diuretics). If monitoring an acute illness, repeat testing as your status stabilizes.
- Below range: <1% often aligns with reduced kidney perfusion (e.g., dehydration, volume loss). Prioritize steady fluid and sodium replacement if you're losing fluids (vomiting/diarrhea/sweat), review medications that can reduce kidney blood flow (e.g., NSAIDs), and reassess after rehydration.
- Above range: >2% often aligns with tubular sodium wasting seen in intrinsic kidney injury or the effect of diuretics. Avoid dehydration and nephrotoxins (e.g., NSAIDs), review timing/dose of diuretics, and track urine output and creatinine trends.
Note: Targets are guides, not medical advice. Adjust based on your symptoms, medical conditions, and clinician recommendations.
How is this calculated?
Evidence baseline:
FENa (%) = (UNa × SCr)/(SNa × UCr) × 100. Typical interpretive cutoffs: <1% suggests prerenal physiology; >2% suggests intrinsic tubular injury; 1–2% is indeterminate and context dependent.
Sized to you:
Your estimate uses your urine sodium (mmol/L) and serum creatinine (mg/dL). When serum sodium and urine creatinine aren't provided, we assume SNa ≈ 140 mmol/L and UCr ≈ 100 mg/dL, so FENa(%) ≈ (UNa × SCr)/140.
Activity adjustment:
Endurance exercise, heat exposure, or low oral intake can lower FENa via volume depletion and hormonal sodium retention. Diuretics (loop/thiazide) raise FENa by increasing urinary sodium losses.
Environment & day-to-day:
Hot/humid climate, high or very low salt intake, GI losses, IV fluids, heart failure, cirrhosis, chronic kidney disease, pregnancy, sepsis, and recent contrast or nephrotoxic drugs can shift FENa and its interpretation.
Why a range?
Tubular sodium handling varies over hours with fluids, meds, and illness. Spot samples and biologic variability make cutoffs probabilistic, so we present ranges rather than a single "perfect" value.
Backed by leading scientific literature
Based on established scientific principles.
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