Emergency · LIVE

Canadian CT Head Rule

Apply the Stiell 2001 Canadian CT Head Rule and return whether CT is indicated from caller-assigned high-risk and medium-risk findings after minor blunt head injury.

LIVE $0.005 USDC GET /api/calc/canadian_ct_head

Markdown: /docs/canadian-ct-head.md · Canonical: https://magentlab.com/docs/canadian-ct-head

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

What it computes

Apply the Stiell 2001 Canadian CT Head Rule and return whether CT is indicated from caller-assigned high-risk and medium-risk findings after minor blunt head injury.

When to use

When an agent has caller-assigned findings after blunt head trauma in a patient 16 or older with GCS 13-15 as published and needs the Canadian CT Head Rule, not PECARN, CATCH, or NEXUS.

When not to use

Not a diagnosis of brain injury. magent does not examine the patient.
This tool is the Stiell 2001 Canadian CT Head Rule only. It is not NEXUS, not PECARN, not CATCH, and not a pediatric head-CT rule (published for age ≥16).
Inclusion as published is blunt trauma with GCS 13-15. magent does not take a GCS integer; the caller assigns the high-risk and medium-risk findings.
Dangerous mechanism is caller-assigned. Published list: pedestrian struck by a motor vehicle, occupant ejected from a motor vehicle, fall from elevation >3 feet or 5 stairs. magent does not classify mechanism.
High-risk factors predict need for neurological intervention. Medium-risk factors detect clinically important brain injury. CT is indicated if either band is met.

Formula

ct indicated if any high-risk (gcs_lt_15_at_2h or suspected_open_or_depressed_skull_fx or any_sign_basal_skull_fx or vomiting_two_or_more or age >= 65) or any medium-risk (amnesia_before_impact_gt_30min or dangerous_mechanism)

Citation

Title: The Canadian CT Head Rule for patients with minor head injury
Authors: Stiell IG, Wells GA, Vandemheen K, et al.
Source: Lancet. 2001;357(9266):1391-1396
DOI: 10.1016/S0140-6736(00)04561-X

Worked example

All findings absent

Given: age=40amnesia_before_impact_gt_30min=falseany_sign_basal_skull_fx=falsedangerous_mechanism=falsegcs_lt_15_at_2h=falsesuspected_open_or_depressed_skull_fx=falsevomiting_two_or_more=false

Age 40 is not a high-risk factor; no high-risk or medium-risk flags
CT is not indicated

Age 65 is high-risk

Given: age=65amnesia_before_impact_gt_30min=falseany_sign_basal_skull_fx=falsedangerous_mechanism=falsegcs_lt_15_at_2h=falsesuspected_open_or_depressed_skull_fx=falsevomiting_two_or_more=false

Age ≥65 is a high-risk factor
CT is indicated

Dangerous mechanism is medium-risk

Given: age=40amnesia_before_impact_gt_30min=falseany_sign_basal_skull_fx=falsedangerous_mechanism=truegcs_lt_15_at_2h=falsesuspected_open_or_depressed_skull_fx=falsevomiting_two_or_more=false

No high-risk factor
Dangerous mechanism is a medium-risk factor (caller-assigned from the paper list)
CT is indicated for clinically important brain injury

Also searched as

Canadian CT Head Rule
Canadian CT Head Injury Rule
CCHR
Stiell CT head
Stiell 2001 head CT
Canadian Head CT Rule
minor head injury CT rule
CIBI CT rule

Try

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

/api/calc/canadian_ct_head?age=40&gcs_lt_15_at_2h=false&suspected_open_or_depressed_skull_fx=false&any_sign_basal_skull_fx=false&vomiting_two_or_more=false&amnesia_before_impact_gt_30min=false&dangerous_mechanism=false

Full URL: https://api.magentlab.com/api/calc/canadian_ct_head?age=40&gcs_lt_15_at_2h=false&suspected_open_or_depressed_skull_fx=false&any_sign_basal_skull_fx=false&vomiting_two_or_more=false&amnesia_before_impact_gt_30min=false&dangerous_mechanism=false

Call

Expect HTTP 402 until you retry with PAYMENT-SIGNATURE. Incomplete query params return HTTP 400 before any quote or charge.

curl -i -H "Accept: application/json" "https://api.magentlab.com/api/calc/canadian_ct_head?age=40&gcs_lt_15_at_2h=false&suspected_open_or_depressed_skull_fx=false&any_sign_basal_skull_fx=false&vomiting_two_or_more=false&amnesia_before_impact_gt_30min=false&dangerous_mechanism=false"

Parameters

Name	Type	Required	Description
`age`	integer	required	Age in years (16-120). Age ≥65 is a high-risk factor that indicates CT; 64 does not. The published rule is for patients ≥16 years.
`gcs_lt_15_at_2h`	boolean	required	GCS <15 at 2 hours after injury. true or false as assigned by the caller. High-risk. magent does not take a GCS integer.
`suspected_open_or_depressed_skull_fx`	boolean	required	Suspected open or depressed skull fracture. true or false as assigned by the caller. High-risk.
`any_sign_basal_skull_fx`	boolean	required	Any sign of basal skull fracture (hemotympanum, raccoon eyes, CSF otorrhea/rhinorrhea, or Battle's sign). true or false as assigned by the caller. High-risk.
`vomiting_two_or_more`	boolean	required	Two or more episodes of vomiting. true or false as assigned by the caller. High-risk.
`amnesia_before_impact_gt_30min`	boolean	required	Amnesia before impact of more than 30 minutes. true or false as assigned by the caller. Medium-risk.
`dangerous_mechanism`	boolean	required	Dangerous mechanism as assigned by the caller. true or false. Medium-risk. Published list: pedestrian struck by a motor vehicle, occupant ejected from a motor vehicle, fall from elevation >3 feet or 5 stairs. magent does not classify mechanism.

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/canadian_ct_head 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": [
    {
      "age": "40",
      "amnesia_before_impact_gt_30min": "false",
      "any_sign_basal_skull_fx": "false",
      "dangerous_mechanism": "false",
      "gcs_lt_15_at_2h": "false",
      "suspected_open_or_depressed_skull_fx": "false",
      "vomiting_two_or_more": "false"
    },
    {
      "age": "40",
      "amnesia_before_impact_gt_30min": "false",
      "any_sign_basal_skull_fx": "false",
      "dangerous_mechanism": "false",
      "gcs_lt_15_at_2h": "false",
      "suspected_open_or_depressed_skull_fx": "false",
      "vomiting_two_or_more": "false"
    }
  ]
}

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/canadian_ct_head",
  "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": "Stiell IG, Wells GA, Vandemheen K, et al.",
        "doi": "10.1016/S0140-6736(00)04561-X",
        "id": "stiell-2001-ct-head",
        "source": "Lancet. 2001;357(9266):1391-1396",
        "title": "The Canadian CT Head Rule for patients with minor head injury"
      },
      "formula": "canadian_ct_head",
      "formula_expression": "ct indicated if any high-risk (gcs_lt_15_at_2h or suspected_open_or_depressed_skull_fx or any_sign_basal_skull_fx or vomiting_two_or_more or age >= 65) or any medium-risk (amnesia_before_impact_gt_30min or dangerous_mechanism)",
      "age_years": 40,
      "criteria": [
        {
          "factor": "gcs_lt_15_at_2h",
          "met": false
        },
        {
          "factor": "suspected_open_or_depressed_skull_fx",
          "met": false
        },
        {
          "factor": "any_sign_basal_skull_fx",
          "met": false
        },
        {
          "factor": "vomiting_two_or_more",
          "met": false
        },
        {
          "value": 40,
          "factor": "age_ge_65",
          "met": false
        },
        {
          "factor": "amnesia_before_impact_gt_30min",
          "met": false
        },
        {
          "factor": "dangerous_mechanism",
          "met": false
        }
      ],
      "ct_indicated": false,
      "high_risk": false,
      "medium_risk": false
    },
    {
      "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": "Stiell IG, Wells GA, Vandemheen K, et al.",
        "doi": "10.1016/S0140-6736(00)04561-X",
        "id": "stiell-2001-ct-head",
        "source": "Lancet. 2001;357(9266):1391-1396",
        "title": "The Canadian CT Head Rule for patients with minor head injury"
      },
      "formula": "canadian_ct_head",
      "formula_expression": "ct indicated if any high-risk (gcs_lt_15_at_2h or suspected_open_or_depressed_skull_fx or any_sign_basal_skull_fx or vomiting_two_or_more or age >= 65) or any medium-risk (amnesia_before_impact_gt_30min or dangerous_mechanism)",
      "age_years": 40,
      "criteria": [
        {
          "factor": "gcs_lt_15_at_2h",
          "met": false
        },
        {
          "factor": "suspected_open_or_depressed_skull_fx",
          "met": false
        },
        {
          "factor": "any_sign_basal_skull_fx",
          "met": false
        },
        {
          "factor": "vomiting_two_or_more",
          "met": false
        },
        {
          "value": 40,
          "factor": "age_ge_65",
          "met": false
        },
        {
          "factor": "amnesia_before_impact_gt_30min",
          "met": false
        },
        {
          "factor": "dangerous_mechanism",
          "met": false
        }
      ],
      "ct_indicated": false,
      "high_risk": false,
      "medium_risk": false
    }
  ]
}

Response

Field	Type	Description
`formula`	string	canadian_ct_head
`formula_expression`	string	Stiell 2001 high-risk or medium-risk CT indication rule
`ct_indicated`	boolean	true when any high-risk or medium-risk factor is met (published imaging rule for clinically important brain injury). Not a diagnosis.
`high_risk`	boolean	true when any high-risk factor is met (GCS <15 at 2 h, suspected open or depressed skull fracture, any basal skull fracture sign, vomiting ≥2, or age ≥65). Predicts need for neurological intervention.
`medium_risk`	boolean	true when any medium-risk factor is met (amnesia before impact >30 min or dangerous mechanism), independent of high_risk
`age_years`	integer	Age used for the ≥65 high-risk factor
`criteria`	array	Per-factor rows with factor and met; age_ge_65 is computed from age (value is age_years)
`citation`	object	Stiell 2001 Lancet citation
`disclaimer`	string	Not-a-device notice

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": "Stiell IG, Wells GA, Vandemheen K, et al.",
    "doi": "10.1016/S0140-6736(00)04561-X",
    "id": "stiell-2001-ct-head",
    "source": "Lancet. 2001;357(9266):1391-1396",
    "title": "The Canadian CT Head Rule for patients with minor head injury"
  },
  "formula": "canadian_ct_head",
  "formula_expression": "ct indicated if any high-risk (gcs_lt_15_at_2h or suspected_open_or_depressed_skull_fx or any_sign_basal_skull_fx or vomiting_two_or_more or age >= 65) or any medium-risk (amnesia_before_impact_gt_30min or dangerous_mechanism)",
  "age_years": 40,
  "criteria": [
    {
      "factor": "gcs_lt_15_at_2h",
      "met": false
    },
    {
      "factor": "suspected_open_or_depressed_skull_fx",
      "met": false
    },
    {
      "factor": "any_sign_basal_skull_fx",
      "met": false
    },
    {
      "factor": "vomiting_two_or_more",
      "met": false
    },
    {
      "value": 40,
      "factor": "age_ge_65",
      "met": false
    },
    {
      "factor": "amnesia_before_impact_gt_30min",
      "met": false
    },
    {
      "factor": "dangerous_mechanism",
      "met": false
    }
  ],
  "ct_indicated": false,
  "high_risk": false,
  "medium_risk": false
}

Client errors (HTTP 400)

Invalid params return 400 without charge. Shared HTTP 402 and 503 meanings: Payments.

HTTP	Code	When
400	`invalid_canadian_ct_age`	age must be an integer from 16 to 120. Returned before settlement; you are not charged.
400	`invalid_flag`	boolean clinical flags must be true or false Returned before settlement; you are not charged.
400	`invalid_items`	POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
400	`invalid_item_count`	items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
400	`invalid_item`	each items entry must be a JSON object Returned before settlement; you are not charged.

Related tools

NEXUS C-spine — Apply the Hoffman 2000 NEXUS C-spine rule and return whether the five low-risk criteria all hold (imaging not indicated by this rule).
Glasgow Coma Scale — Compute the Glasgow Coma Scale as the sum of caller-assigned eye, verbal, and motor integers. The 1974 or 1976 edition is required.

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. Stdio MCP: /docs/mcp.

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.