LIVE

Stool osmotic gap

Compute the Eherer–Fordtran fecal osmotic gap from stool sodium and potassium, using measured stool osmolality when supplied or 290 mOsm/kg when omitted.

LIVE $0.005 USDC GET /api/calc/stool_osmotic_gap

Markdown: /docs/stool-osmotic-gap.md · Canonical: https://magentlab.com/docs/stool-osmotic-gap

Not a medical device. Not a diagnosis, dose, or listing recommendation.

What it computes

Compute the Eherer–Fordtran fecal osmotic gap from stool sodium and potassium, using measured stool osmolality when supplied or 290 mOsm/kg when omitted.

When to use

When an agent needs the published fecal osmotic-gap arithmetic and must not invent an osmotic-versus-secretory diagnosis.

When not to use

• Not a diagnosis of osmotic versus secretory diarrhea. gap_gt_50 flags whether the gap exceeds the paper’s ~50 mOsm/kg separator; it is not a clinical classification.
• When measured stool osmolality is omitted, 290 mOsm/kg is assumed. A negative gap is returned when 2×(Na+K) exceeds the osmolality used (for example from laboratory error) and is not rejected.

Formula

osmotic_gap = stool_osm_mosm_kg - 2 * (stool_sodium_mmol_l + stool_potassium_mmol_l)

Citation

Title

Fecal osmotic gap and pH in experimental diarrhea of various causes

Authors

Eherer AJ, Fordtran JS

Source

Gastroenterology. 1992;103(2):545-551

DOI

10.1016/0016-5085(92)90845-P

Worked example

Try

Opens the live endpoint. Unpaid browser requests show the paywall; agents should send Accept: application/json.

/api/calc/stool_osmotic_gap?stool_sodium_mmol_l=30&stool_potassium_mmol_l=75

Full URL: https://api.magentlab.com/api/calc/stool_osmotic_gap?stool_sodium_mmol_l=30&stool_potassium_mmol_l=75

x402 V2 curl

Expect HTTP 402 and a PAYMENT-REQUIRED header until you retry with PAYMENT-SIGNATURE. Incomplete query params return HTTP 400 before any quote or charge. HTTP 503 after a signature: retry the same PAYMENT-SIGNATURE — that is not a new 402.

curl -i -H "Accept: application/json" "https://api.magentlab.com/api/calc/stool_osmotic_gap?stool_sodium_mmol_l=30&stool_potassium_mmol_l=75"

Cursor mcp.json

Intended config for @magent/mcp. This is not npm @x402/fetch (a payment fetch wrapper).

{
  "mcpServers": {
    "magent": {
      "args": [
        "-y",
        "@magent/mcp"
      ],
      "command": "npx",
      "env": {
        "X402_PRIVATE_KEY": "0xYOUR_SPENDING_KEY"
      }
    }
  }
}

Parameters

Bulk (POST)

POST the same path with a JSON items array. Price is n times the GET unit. Invalid items return HTTP 400 before settlement.

POST /api/calc/stool_osmotic_gap Max 25 unit_amount * n PREVIEW

• 1 to 25 items. Each item uses the same keys as the GET query parameters.
• The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
• HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
• Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
• x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request (fixture)

{
  "items": [
    {
      "stool_potassium_mmol_l": "75",
      "stool_sodium_mmol_l": "30"
    },
    {
      "stool_potassium_mmol_l": "75",
      "stool_sodium_mmol_l": "30"
    }
  ]
}

Open bulk paywall →

Opens a two-item fixture on the API host. Unpaid browsers get the same MetaMask paywall as GET; Pay retries POST with those items.

Example 200 (fixture)

{
  "count": 2,
  "path": "/api/calc/stool_osmotic_gap",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Eherer AJ, Fordtran JS",
        "doi": "10.1016/0016-5085(92)90845-P",
        "id": "eherer-fordtran-1992",
        "source": "Gastroenterology. 1992;103(2):545-551",
        "title": "Fecal osmotic gap and pH in experimental diarrhea of various causes"
      },
      "formula": "eherer_fordtran",
      "formula_expression": "osmotic_gap = stool_osm_mosm_kg - 2 * (stool_sodium_mmol_l + stool_potassium_mmol_l)",
      "assumed_osmolality": true,
      "gap_gt_50": true,
      "osmotic_gap": 80.0,
      "stool_osm_mosm_kg": 290.0,
      "stool_potassium_mmol_l": 75.0,
      "stool_sodium_mmol_l": 30.0
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Eherer AJ, Fordtran JS",
        "doi": "10.1016/0016-5085(92)90845-P",
        "id": "eherer-fordtran-1992",
        "source": "Gastroenterology. 1992;103(2):545-551",
        "title": "Fecal osmotic gap and pH in experimental diarrhea of various causes"
      },
      "formula": "eherer_fordtran",
      "formula_expression": "osmotic_gap = stool_osm_mosm_kg - 2 * (stool_sodium_mmol_l + stool_potassium_mmol_l)",
      "assumed_osmolality": true,
      "gap_gt_50": true,
      "osmotic_gap": 80.0,
      "stool_osm_mosm_kg": 290.0,
      "stool_potassium_mmol_l": 75.0,
      "stool_sodium_mmol_l": 30.0
    }
  ]
}

Response

Example JSON

Machine form of the same example. Frozen fixture. Not a live lookup.

{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Eherer AJ, Fordtran JS",
    "doi": "10.1016/0016-5085(92)90845-P",
    "id": "eherer-fordtran-1992",
    "source": "Gastroenterology. 1992;103(2):545-551",
    "title": "Fecal osmotic gap and pH in experimental diarrhea of various causes"
  },
  "formula": "eherer_fordtran",
  "formula_expression": "osmotic_gap = stool_osm_mosm_kg - 2 * (stool_sodium_mmol_l + stool_potassium_mmol_l)",
  "assumed_osmolality": true,
  "gap_gt_50": true,
  "osmotic_gap": 80.0,
  "stool_osm_mosm_kg": 290.0,
  "stool_potassium_mmol_l": 75.0,
  "stool_sodium_mmol_l": 30.0
}

Errors

Related tools

• Serum osmolality — Compute Worthley calculated serum osmolality from sodium, glucose, and BUN, plus an optional osmolar gap when a measured osm is supplied.

Also searched as

• fecal osmotic gap
• stool osmotic gap
• stool osmolar gap
• fecal osm gap
• Eherer Fordtran gap
• stool sodium potassium gap

Payment

Required query parameters must be present and valid. Invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s. Unpaid valid requests return HTTP 402 with a base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote: retry the same PAYMENT-SIGNATURE. Full handshake and shared payment errors: Payments.

Guarantees

• Invalid query parameters return HTTP 400 before settlement. You are not charged.
• Settlement finishes before the tool executes (paymentFlow upfront). Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
• HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
• Execution is timeout-bounded and concurrency-capped.
• Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.