FENa Calculator
Calculate the fractional excretion of sodium (FENa) from urine and plasma sodium and creatinine, with an interpretation to help tell prerenal azotemia from acute tubular necrosis.
Input
mmol/L or mEq/L — same unit as plasma sodium
Same unit as plasma creatinine (e.g. mg/dL)
Output
| Metric | Value |
|---|---|
| No data yet | |
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/fena-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"urineSodium": "40",
"plasmaSodium": "140",
"urineCreatinine": "50",
"plasmaCreatinine": "1.0"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `fena-calculator` tool (FENa Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/fena-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="FENa Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
What is FENa?
The fractional excretion of sodium (FENa) is the percentage of filtered sodium that ends up in the urine. It is used in acute kidney injury to help separate prerenal azotemia (kidneys under-perfused but working) from acute tubular necrosis (damaged tubules that can't reabsorb sodium).
Formula
FENa (%) = (urine Na × plasma creatinine) ÷ (plasma Na × urine creatinine) × 100
Sodium values must share a unit, and so must the two creatinine values — the units cancel out.
Interpreting the result
| FENa | Suggests |
|---|---|
| < 1% | Prerenal cause |
| 1–2% | Indeterminate |
| > 2% | Intrinsic renal cause (e.g. ATN) |
Limitations
FENa is unreliable in patients on diuretics, with chronic kidney disease, or with contrast or glomerular disease; FEUrea is often preferred with diuretics. This tool is educational and not a substitute for clinical judgment.
All calculation happens in your browser — no values are sent anywhere.