Health
Free Water Clearance Calculator
Calculate solute-free water clearance (C_H₂O) and electrolyte-free water clearance (eC_H₂O) to differentiate hypo-/hypernatremia. Classic: C_H₂O = V·(1 − U_osm/P_osm); positive = dilute urine excreting free water (diabetes insipidus, polydipsia, water-load recovery), negative = concentrated urine conserving free water (dehydration, SIADH). Electrolyte-free: eC_H₂O = V·(1 − (U_Na + U_K)/P_Na), which better predicts the direction of serum sodium change — a negative eC_H₂O means the urine is electrolyte-free-water-rich and tends to raise serum Na⁺, informing IV fluid choice. Optional Na/K inputs enable the electrolyte-free calculation. Derived from Rose, Shimizu 2002 (Nephron), and NephSIM. Point estimate; interpret with full clinical context. Not medical advice.
Quick start
Call this tool from your code in three languages.
curl -X POST 'https://api.elysiatools.com/en/api/tools/free-water-clearance' \
-H 'Content-Type: application/json' \
-d '{"urineFlow":1,"urineOsm":600,"plasmaOsm":260,"urineSodium":0,"urinePotassium":0,"serumSodium":0,"decimalPlaces":4}'API reference
Send a POST request with your inputs as JSON. File parameters require a separate upload first.
Endpoint
POST https://api.elysiatools.com/en/api/tools/free-water-clearanceParameters
| Name | Type | Required | Description |
|---|---|---|---|
| urineFlow | number | Yes | Urine flow rate V (volume per unit time). Must be positive. Use any consistent per-time unit; output shares it. |
| urineOsm | number | Yes | Urine osmolality U_osm. Must be positive. |
| plasmaOsm | number | Yes | Plasma osmolality P_osm. Must be positive. |
| urineSodium | number | No | Optional urine sodium U_Na (mmol/L) for the electrolyte-free water clearance. Must be ≥0. |
| urinePotassium | 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:
{
"mcpServers": {
"elysiatools-free-water-clearance": {
"name": "free-water-clearance",
"description": "Calculate solute-free water clearance (C_H₂O) and electrolyte-free water clearance (eC_H₂O) to differentiate hypo-/hypernatremia. Classic: C_H₂O = V·(1 − U_osm/P_osm); positive = dilute urine excreting free water (diabetes insipidus, polydipsia, water-load recovery), negative = concentrated urine conserving free water (dehydration, SIADH). Electrolyte-free: eC_H₂O = V·(1 − (U_Na + U_K)/P_Na), which better predicts the direction of serum sodium change — a negative eC_H₂O means the urine is electrolyte-free-water-rich and tends to raise serum Na⁺, informing IV fluid choice. Optional Na/K inputs enable the electrolyte-free calculation. Derived from Rose, Shimizu 2002 (Nephron), and NephSIM. Point estimate; interpret with full clinical context. Not medical advice.",
"baseUrl": "https://api.elysiatools.com/mcp/sse?toolId=free-water-clearance",
"command": "",
"args": [],
"env": {},
"isActive": true,
"type": "sse"
}
}
}List available tools
After connecting to the SSE endpoint, list the exposed tools:
{
"jsonrpc": "2.0",
"id": 1,
"method": "tools/list"
}Call this tool
Invoke the tool by its id, passing arguments built from its parameters:
{
"jsonrpc": "2.0",
"id": 2,
"method": "tools/call",
"params": {
"name": "free-water-clearance",
"arguments": {
"urineFlow": 1,
"urineOsm": 600,
"plasmaOsm": 260,
"urineSodium": 0,
"urinePotassium": 0,
"serumSodium": 0,
"decimalPlaces": 4
}
}
}