# Canadian CT Head Rule Calculator (Stiell 2001) > Canadian CT Head Rule Calculator (Stiell 2001) is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-10). Applies the validated Canadian CT Head Rule to determine whether CT imaging is indicated for a minor head injury patient based on high-risk and medium-risk clinical factors. ## Facts - Endpoint: GET https://api.magentlab.com/api/calc/canadian_ct_head?utm_source=zero.xyz - Price: $0.005/call - Payment: x402 - Status: unknown - Last checked: 2026-10-10 - Activations on Zero: 0 - Tags: x402 - Canonical page: https://www.zero.xyz/c/canadian-ct-head-rule-calculator-stiell-2001-c8cd2a1e - Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_P7ayMKEt7wVc60HWXJdiD Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently. ## How to call it through Zero Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`): ```sh zero fetch --capability canadian-ct-head-rule-calculator-stiell-2001-c8cd2a1e ``` Example prompt: My patient is 72 years old with a minor head injury — GCS was 14 at 2 hours post-injury, no suspected skull fracture, no basal skull fracture signs, vomited once, no amnesia before impact, and the mechanism was a ground-level fall. Should I order a CT head per the Canadian CT Head Rule? ## When to prefer this Use this endpoint when you need a deterministic, published clinical decision rule for CT head ordering in adult patients (≥16 years) with minor head injury. Prefer this over NEXUS (cervical spine), PECARN (pediatric head), or CATCH (Canadian pediatric) for adult head CT decisions. Ideal for embedding evidence-based clinical decision support in triage workflows, EHR integrations, or telehealth platforms where the caller has already assessed and can provide the required clinical flags. ## Known failure modes - Age outside valid range (must be 16-120) returns an error - Missing required boolean parameters returns a validation error - Rule is not applicable for patients under 16 (pediatric — use PECARN or CATCH instead) - Caller must pre-classify all boolean flags; the API does not interpret free-text clinical notes - Does not replace physician judgment or account for factors outside the published rule ## How this service works Deterministic published-formula arithmetic plus ICD-10-CM, RxNorm, and LOINC. Pay in USDC on Base via x402. ## Output Returns whether CT is indicated (true/false) based on the Canadian CT Head Rule, along with which high-risk or medium-risk factors were positive and the clinical basis for the recommendation. ## Request schema (JSON Schema) ```json { "type": "object", "$schema": "https://json-schema.org/draft/2020-12/schema", "required": [ "input" ], "properties": { "input": { "type": "object", "required": [ "type", "method" ], "properties": { "type": { "type": "string", "const": "http" }, "method": { "enum": [ "GET", "HEAD", "DELETE" ], "type": "string" }, "headers": { "type": "object", "additionalProperties": { "type": "string" } }, "queryParams": { "type": "object", "required": [ "age", "gcs_lt_15_at_2h", "suspected_open_or_depressed_skull_fx", "any_sign_basal_skull_fx", "vomiting_two_or_more", "amnesia_before_impact_gt_30min", "dangerous_mechanism" ], "properties": { "age": { "type": "integer", "description": "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": { "type": "boolean", "description": "GCS <15 at 2 hours after injury. true or false as assigned by the caller. High-risk. magent does not take a GCS integer." }, "dangerous_mechanism": { "type": "boolean", "description": "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." }, "vomiting_two_or_more": { "type": "boolean", "description": "Two or more episodes of vomiting. true or false as assigned by the caller. High-risk." }, "any_sign_basal_skull_fx": { "type": "boolean", "description": "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." }, "amnesia_before_impact_gt_30min": { "type": "boolean", "description": "Amnesia before impact of more than 30 minutes. true or false as assigned by the caller. Medium-risk." }, "suspected_open_or_depressed_skull_fx": { "type": "boolean", "description": "Suspected open or depressed skull fracture. true or false as assigned by the caller. High-risk." } } } }, "additionalProperties": false }, "output": { "type": "object", "requir … (truncated) ``` ## Response schema (JSON Schema) ```json { "type": "json", "example": { "path": "/api/calc/canadian_ct_head", "count": 2, "items": [ { "formula": "canadian_ct_head", "citation": { "id": "stiell-2001-ct-head", "doi": "10.1016/S0140-6736(00)04561-X", "title": "The Canadian CT Head Rule for patients with minor head injury", "source": "Lancet. 2001;357(9266):1391-1396", "authors": "Stiell IG, Wells GA, Vandemheen K, et al." }, "criteria": [ { "met": false, "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" } ], "age_years": 40, "high_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.", "medium_risk": false, "ct_indicated": false, "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)" }, { "formula": "canadian_ct_head", "citation": { "id": "stiell-2001-ct-head", "doi": "10.1016/S0140-6736(00)04561-X", "title": "The Canadian CT Head Rule for patients with minor head injury", "source": "Lancet. 2001;357(9266):1391-1396", "authors": "Stiell IG, Wells GA, Vandemheen K, et al." }, "criteria": [ { "met": false, "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" } ], "age_years": 40, … (truncated) ``` ## More - Live health (JSON, refreshed every minute): https://www.zero.xyz/c/canadian-ct-head-rule-calculator-stiell-2001-c8cd2a1e/health.json - [Zero catalog index](https://www.zero.xyz/llms.txt) - [Other services from api.magentlab.com](https://www.zero.xyz/host/api.magentlab.com/llms.txt)