Health

Fractional Excretion of Sodium (FENa)

Calculate the Fractional Excretion of Sodium (FENa) to differentiate prerenal from intrinsic acute kidney injury: FENa (%) = [U_Na × S_Cr] / [S_Na × U_Cr] × 100. In oliguric AKI, FENa <1% suggests prerenal azotemia (sodium-avid state: volume depletion, heart failure, hepatorenal syndrome), while FENa ≥1% suggests intrinsic injury (typically ATN). FENa >4% is sometimes cited as supportive of post-obstructive pathology. Caveats: unreliable on diuretics (use FEUrea <35%), contrast/sepsis ATN can present with low FENa, chronic CKD and glucosuria elevate FENa independently. Derived from Espinel CH, JAMA 1976. Most useful in oliguric AKI; interpret with full clinical context. Not medical advice.

json· JSON resultOpen tool

Quick start

Call this tool from your code in three languages.

cURL

curl -X POST 'https://api.elysiatools.com/en/api/tools/fractional-excretion-sodium' \
  -H 'Content-Type: application/json' \
  -d '{"urineSodium":20,"serumCreatinine":1.5,"serumSodium":140,"urineCreatinine":120,"decimalPlaces":4}'

API reference

Send a POST request with your inputs as JSON. File parameters require a separate upload first.

Endpoint

HTTP

POST https://api.elysiatools.com/en/api/tools/fractional-excretion-sodium

Parameters

Name	Type	Required	Description
urineSodium	number	Yes	Urine sodium concentration in mmol/L. Must be ≥0.
serumCreatinine	number	Yes	Serum creatinine in mg/dL. Must be positive.
serumSodium	number	Yes	Serum sodium concentration in mmol/L. Must be positive.
urineCreatinine	number	Yes	Urine creatinine concentration in mg/dL. Must be positive.
decimalPlaces	number

MCP integration

Add this tool to your Model Context Protocol server so AI agents can list and call it.

Server configuration

Add this block to your MCP client configuration:

mcp.json

{
  "mcpServers": {
    "elysiatools-fractional-excretion-sodium": {
      "name": "fractional-excretion-sodium",
      "description": "Calculate the Fractional Excretion of Sodium (FENa) to differentiate prerenal from intrinsic acute kidney injury: FENa (%) = [U_Na × S_Cr] / [S_Na × U_Cr] × 100. In oliguric AKI, FENa <1% suggests prerenal azotemia (sodium-avid state: volume depletion, heart failure, hepatorenal syndrome), while FENa ≥1% suggests intrinsic injury (typically ATN). FENa >4% is sometimes cited as supportive of post-obstructive pathology. Caveats: unreliable on diuretics (use FEUrea <35%), contrast/sepsis ATN can present with low FENa, chronic CKD and glucosuria elevate FENa independently. Derived from Espinel CH, JAMA 1976. Most useful in oliguric AKI; interpret with full clinical context. Not medical advice.",
      "baseUrl": "https://api.elysiatools.com/mcp/sse?toolId=fractional-excretion-sodium",
      "command": "",
      "args": [],
      "env": {},
      "isActive": true,
      "type": "sse"
    }
  }
}

List available tools

After connecting to the SSE endpoint, list the exposed tools:

tools/list

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/list"
}

Call this tool

Invoke the tool by its id, passing arguments built from its parameters:

tools/call

{
  "jsonrpc": "2.0",
  "id": 2,
  "method": "tools/call",
  "params": {
    "name": "fractional-excretion-sodium",
    "arguments": {
  "urineSodium": 20,
  "serumCreatinine": 1.5,
  "serumSodium": 140,
  "urineCreatinine": 120,
  "decimalPlaces": 4
}
  }
}

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