# CATCH

CATCH

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/catch`
HTML: https://magentlab.com/docs/catch
Markdown: https://magentlab.com/docs/catch.md

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

## What it computes

Apply the Osmond 2010 CATCH derivation and return high, medium, or low risk plus whether CT of the head is indicated from seven caller-assigned findings after pediatric minor head injury.

## When to use

When an agent has caller-assigned findings after minor head injury in a child and needs the Osmond 2010 CATCH CT rule, not PECARN, CHALICE, Canadian CT Head, NEXUS, or CATCH-2.

## When not to use

- Not a medical device. Not a diagnosis. magent does not examine the child or read CT.
- This tool is the Osmond 2010 CATCH derivation only. It is not CATCH-2 (2018) and does not use CATCH-2 refinement items or cutoffs.
- Not PECARN, not CHALICE, not the Canadian CT Head Rule, and not NEXUS.
- Derivation enrolled children 0-16 years with minor head injury (GCS 13-15 plus loss of consciousness, amnesia, disorientation, persistent vomiting, or irritability). magent does not take numeric age.
- The caller assigns all seven findings. Dangerous mechanism is caller-assigned (paper examples: motor vehicle collision, fall from elevation ≥3 ft / ≥91 cm or 5 stairs, fall from bicycle with no helmet). magent does not classify mechanism.

## Formula

```
high if any of gcs_lt_15_at_2h, suspected_open_or_depressed_skull_fracture, worsening_headache, irritability; else medium if any of basal_skull_fracture, large_boggy_scalp_hematoma, dangerous_mechanism; else low; CT indicated if high or medium
```

## Citation

[CATCH: a clinical decision rule for the use of computed tomography in children with minor head injury](https://doi.org/10.1503/cmaj.091421)
Osmond MH, Klassen TP, Wells GA, et al.
CMAJ. 2010;182(4):341-348
DOI: [10.1503/cmaj.091421](https://doi.org/10.1503/cmaj.091421)

## Worked example

### All seven findings absent

Given: `basal_skull_fracture=false, dangerous_mechanism=false, gcs_lt_15_at_2h=false, irritability=false, large_boggy_scalp_hematoma=false, suspected_open_or_depressed_skull_fracture=false, worsening_headache=false`

1. No high-risk finding (GCS <15 at 2 h, open or depressed skull fracture, worsening headache, irritability)
2. No medium-risk finding (basal skull fracture, large boggy scalp hematoma, dangerous mechanism)
3. CATCH low risk; CT is not indicated


### GCS <15 at two hours is high risk

Given: `basal_skull_fracture=false, dangerous_mechanism=false, gcs_lt_15_at_2h=true, irritability=false, large_boggy_scalp_hematoma=false, suspected_open_or_depressed_skull_fracture=false, worsening_headache=false`

1. GCS <15 at two hours is a high-risk finding (need for neurologic intervention)
2. CATCH high risk; CT is indicated


### Dangerous mechanism is medium risk

Given: `basal_skull_fracture=false, dangerous_mechanism=true, gcs_lt_15_at_2h=false, irritability=false, large_boggy_scalp_hematoma=false, suspected_open_or_depressed_skull_fracture=false, worsening_headache=false`

1. No high-risk finding
2. Dangerous mechanism is a medium-risk finding as assigned by the caller (paper examples: MVC, fall ≥3 ft / ≥91 cm or 5 stairs, unhelmeted bicycle fall)
3. CATCH medium risk; CT is indicated for brain injury on CT


## Also searched as

- CATCH rule
- CATCH head CT
- Osmond CATCH
- Canadian Assessment of Tomography for Childhood Head injury
- CATCH 2010
- pediatric CATCH CT
- Osmond 2010 CATCH
- childhood head injury CT rule

## Parameters

- `gcs_lt_15_at_2h` (boolean, required): GCS score <15 at two hours after injury. true or false as assigned by the caller. High-risk (need for neurologic intervention). magent does not take a GCS integer.
- `suspected_open_or_depressed_skull_fracture` (boolean, required): Suspected open or depressed skull fracture. true or false as assigned by the caller. High-risk (need for neurologic intervention). magent does not examine the child.
- `worsening_headache` (boolean, required): History of worsening headache. true or false as assigned by the caller. High-risk (need for neurologic intervention).
- `irritability` (boolean, required): Irritability on examination. true or false as assigned by the caller. High-risk (need for neurologic intervention). magent does not examine the child.
- `basal_skull_fracture` (boolean, required): Any sign of basal skull fracture. true or false as assigned by the caller. Medium-risk (brain injury on CT). magent does not examine the child.
- `large_boggy_scalp_hematoma` (boolean, required): Large, boggy hematoma of the scalp. true or false as assigned by the caller. Medium-risk (brain injury on CT). magent does not examine the child.
- `dangerous_mechanism` (boolean, required): Dangerous mechanism of injury as assigned by the caller. true or false. Medium-risk (brain injury on CT). Paper examples: motor vehicle collision, fall from elevation ≥3 ft / ≥91 cm or 5 stairs, fall from bicycle with no helmet. magent does not classify mechanism.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/catch`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- 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:

```json
{
  "items": [
    {
      "basal_skull_fracture": "false",
      "dangerous_mechanism": "false",
      "gcs_lt_15_at_2h": "false",
      "irritability": "false",
      "large_boggy_scalp_hematoma": "false",
      "suspected_open_or_depressed_skull_fracture": "false",
      "worsening_headache": "false"
    },
    {
      "basal_skull_fracture": "false",
      "dangerous_mechanism": "false",
      "gcs_lt_15_at_2h": "false",
      "irritability": "false",
      "large_boggy_scalp_hematoma": "false",
      "suspected_open_or_depressed_skull_fracture": "false",
      "worsening_headache": "false"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/catch

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/catch",
  "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": "Osmond MH, Klassen TP, Wells GA, et al.",
        "doi": "10.1503/cmaj.091421",
        "id": "osmond-2010",
        "pmid": "20142371",
        "source": "CMAJ. 2010;182(4):341-348",
        "title": "CATCH: a clinical decision rule for the use of computed tomography in children with minor head injury"
      },
      "formula": "catch",
      "formula_expression": "high if any of gcs_lt_15_at_2h, suspected_open_or_depressed_skull_fracture, worsening_headache, irritability; else medium if any of basal_skull_fracture, large_boggy_scalp_hematoma, dangerous_mechanism; else low; CT indicated if high or medium",
      "criteria": [
        {
          "factor": "gcs_lt_15_at_2h",
          "met": false
        },
        {
          "factor": "suspected_open_or_depressed_skull_fracture",
          "met": false
        },
        {
          "factor": "worsening_headache",
          "met": false
        },
        {
          "factor": "irritability",
          "met": false
        },
        {
          "factor": "basal_skull_fracture",
          "met": false
        },
        {
          "factor": "large_boggy_scalp_hematoma",
          "met": false
        },
        {
          "factor": "dangerous_mechanism",
          "met": false
        }
      ],
      "ct_indicated": false,
      "catch_high_risk": false,
      "catch_low_risk": true,
      "catch_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": "Osmond MH, Klassen TP, Wells GA, et al.",
        "doi": "10.1503/cmaj.091421",
        "id": "osmond-2010",
        "pmid": "20142371",
        "source": "CMAJ. 2010;182(4):341-348",
        "title": "CATCH: a clinical decision rule for the use of computed tomography in children with minor head injury"
      },
      "formula": "catch",
      "formula_expression": "high if any of gcs_lt_15_at_2h, suspected_open_or_depressed_skull_fracture, worsening_headache, irritability; else medium if any of basal_skull_fracture, large_boggy_scalp_hematoma, dangerous_mechanism; else low; CT indicated if high or medium",
      "criteria": [
        {
          "factor": "gcs_lt_15_at_2h",
          "met": false
        },
        {
          "factor": "suspected_open_or_depressed_skull_fracture",
          "met": false
        },
        {
          "factor": "worsening_headache",
          "met": false
        },
        {
          "factor": "irritability",
          "met": false
        },
        {
          "factor": "basal_skull_fracture",
          "met": false
        },
        {
          "factor": "large_boggy_scalp_hematoma",
          "met": false
        },
        {
          "factor": "dangerous_mechanism",
          "met": false
        }
      ],
      "ct_indicated": false,
      "catch_high_risk": false,
      "catch_low_risk": true,
      "catch_medium_risk": false
    }
  ]
}
```

## Response fields

- `formula` (string): catch
- `formula_expression` (string): Osmond 2010 CATCH high then medium then low CT indication rule
- `catch_high_risk` (boolean): true when any high-risk finding is present (GCS <15 at 2 h, suspected open or depressed skull fracture, worsening headache, or irritability). Predicts need for neurologic intervention. Not a diagnosis.
- `catch_medium_risk` (boolean): true when any medium-risk finding is present (basal skull fracture sign, large boggy scalp hematoma, or dangerous mechanism) and no high-risk finding is present. Predicts brain injury on CT. Not a diagnosis.
- `catch_low_risk` (boolean): true when none of the seven published findings is present
- `ct_indicated` (boolean): true when catch_high_risk or catch_medium_risk is true (any of the seven findings). Not a diagnosis.
- `criteria` (array): Per-factor rows with factor and met; met is true when that Osmond 2010 CATCH finding is present
- `citation` (object): Osmond 2010 CMAJ citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "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": "Osmond MH, Klassen TP, Wells GA, et al.",
    "doi": "10.1503/cmaj.091421",
    "id": "osmond-2010",
    "pmid": "20142371",
    "source": "CMAJ. 2010;182(4):341-348",
    "title": "CATCH: a clinical decision rule for the use of computed tomography in children with minor head injury"
  },
  "formula": "catch",
  "formula_expression": "high if any of gcs_lt_15_at_2h, suspected_open_or_depressed_skull_fracture, worsening_headache, irritability; else medium if any of basal_skull_fracture, large_boggy_scalp_hematoma, dangerous_mechanism; else low; CT indicated if high or medium",
  "criteria": [
    {
      "factor": "gcs_lt_15_at_2h",
      "met": false
    },
    {
      "factor": "suspected_open_or_depressed_skull_fracture",
      "met": false
    },
    {
      "factor": "worsening_headache",
      "met": false
    },
    {
      "factor": "irritability",
      "met": false
    },
    {
      "factor": "basal_skull_fracture",
      "met": false
    },
    {
      "factor": "large_boggy_scalp_hematoma",
      "met": false
    },
    {
      "factor": "dangerous_mechanism",
      "met": false
    }
  ],
  "ct_indicated": false,
  "catch_high_risk": false,
  "catch_low_risk": true,
  "catch_medium_risk": false
}
```

## Errors

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

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [PECARN pediatric head CT](https://magentlab.com/docs/pecarn-head) — Apply the Kuppermann 2009 PECARN prediction trees and return high, intermediate, or low risk of clinically important brain injury from caller-assigned findings after pediatric head trauma.
- [CHALICE](https://magentlab.com/docs/chalice) — Apply the Dunning 2006 CHALICE rule and return whether CT is required from caller-assigned history, examination, and mechanism findings after head injury in a child younger than 16.
- [Canadian CT Head Rule](https://magentlab.com/docs/canadian-ct-head) — 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.
- [New Orleans Head CT Rule](https://magentlab.com/docs/new-orleans-head) — Apply the Haydel 2000 New Orleans Head CT Rule and return whether CT is indicated from age and six caller-assigned findings after minor head injury.

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, 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.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. 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.