Health

Osmolar Gap Calculator

Calculate the osmolar gap (osmolal gap, OG) = measured serum osmolality − calculated osmolality. Calculated osmolality uses the conventional formula 2 × Na + Glucose/18 + BUN/2.8 (mg/dL) or the SI formula 2 × Na + Glucose + Urea (mmol/L). A normal OG is approximately −10 to +10 mOsm/kg. An elevated OG indicates unmeasured osmoles — ethanol; toxic alcohols (methanol, ethylene glycol, diethylene glycol, propylene glycol); mannitol, sorbitol, glycerol; severe DKA; sepsis/end-stage renal disease. An optional ethanol level computes the ethanol-corrected gap (OG_corr = OG − EtOH/4.6) to reveal a residual unmeasured osmole such as methanol or ethylene glycol. A normal OG does NOT exclude late-stage toxic-alcohol poisoning (the parent compound is metabolized to acids, raising the anion gap instead). Derived from Kraut 2024, Whittington 2009, and MDCalc. Interpret with anion gap, blood gas, and history. Not medical advice.

json· JSON resultOpen tool

Quick start

Call this tool from your code in three languages.

cURL

curl -X POST 'http://127.0.0.1:3003/en/api/tools/osmolar-gap-calculator' \
  -H 'Content-Type: application/json' \
  -d '{"unitSystem":"conventional","measuredOsm":330,"sodium":140,"glucose":110,"bunOrUrea":14,"ethanol":0,"decimalPlaces":1}'

API reference

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

Endpoint

HTTP

POST http://127.0.0.1:3003/en/api/tools/osmolar-gap-calculator

Parameters

Name	Type	Required	Description
unitSystem	select	Yes	—
measuredOsm	number	Yes	Measured serum osmolality by freezing-point depression (mOsm/kg).
sodium	number	Yes	Serum sodium (mmol/L), always in mmol/L regardless of unit system.
glucose	number	Yes	Serum glucose. mg/dL under Conventional units, mmol/L under SI units.
bunOrUrea	number	Yes

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-osmolar-gap-calculator": {
      "name": "osmolar-gap-calculator",
      "description": "Calculate the osmolar gap (osmolal gap, OG) = measured serum osmolality − calculated osmolality. Calculated osmolality uses the conventional formula 2 × Na + Glucose/18 + BUN/2.8 (mg/dL) or the SI formula 2 × Na + Glucose + Urea (mmol/L). A normal OG is approximately −10 to +10 mOsm/kg. An elevated OG indicates unmeasured osmoles — ethanol; toxic alcohols (methanol, ethylene glycol, diethylene glycol, propylene glycol); mannitol, sorbitol, glycerol; severe DKA; sepsis/end-stage renal disease. An optional ethanol level computes the ethanol-corrected gap (OG_corr = OG − EtOH/4.6) to reveal a residual unmeasured osmole such as methanol or ethylene glycol. A normal OG does NOT exclude late-stage toxic-alcohol poisoning (the parent compound is metabolized to acids, raising the anion gap instead). Derived from Kraut 2024, Whittington 2009, and MDCalc. Interpret with anion gap, blood gas, and history. Not medical advice.",
      "baseUrl": "http://127.0.0.1:3003/mcp/sse?toolId=osmolar-gap-calculator",
      "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": "osmolar-gap-calculator",
    "arguments": {
  "unitSystem": "conventional",
  "measuredOsm": 330,
  "sodium": 140,
  "glucose": 110,
  "bunOrUrea": 14,
  "ethanol": 0,
  "decimalPlaces": 1
}
  }
}

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