# CHIP prediction rule

CHIP

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

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

## What it computes

Apply the Smits 2007 simple CHIP rule and return whether CT is indicated from caller-assigned major and minor findings plus GCS and age after minor 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 2007 simple CHIP rule, not Canadian CT Head, NEXUS Head CT, PECARN, New Orleans, or the 2022 CHIP update.

## When not to use

- Not a medical device. Not a diagnosis of intracranial injury. magent does not examine the patient.
- magent does not interpret imaging or order a CT. This tool returns whether CT is indicated by the published simple CHIP rule only.
- Smits 2007 simple rule only (CT if ≥1 major or ≥2 minor). Not the detailed CHIP logistic model and not the 2022 CHIP update (different coefficients; drops anticoagulants; adds antiplatelet).
- Not the Canadian CT Head Rule, not NEXUS Head CT, not New Orleans, and not PECARN. Published for adults ≥16 years with GCS 13-15.
- The caller assigns every clinical flag. GCS is an integer 13-15. Age is an integer ≥16. magent does not assign GCS, classify mechanism, or read a coagulation assay.
- PTA ≥4 h is major; PTA of 2 to <4 h is minor. GCS deterioration ≥2 points at 1 hour is major; 1 point is minor. Age ≥60 is major; age 40-59 is the 40-60 y minor band.

## Formula

```
ct indicated if ≥1 major (pedestrian_or_cyclist_vs_vehicle, ejected_from_vehicle, vomiting, pta_ge_4h, clinical_signs_skull_fracture, gcs < 15, gcs_deterioration_ge_2, anticoagulant_therapy, posttraumatic_seizure, age ≥ 60) or ≥2 minor (fall_from_any_elevation, persistent_anterograde_amnesia, pta_2_to_lt_4h, skull_contusion, neurologic_deficit, loss_of_consciousness, gcs_deterioration_1, age 40-60)
```

## Citation

[Predicting intracranial traumatic findings on computed tomography in patients with minor head injury: the CHIP prediction rule](https://doi.org/10.7326/0003-4819-146-6-200703200-00004)
Smits M, Dippel DW, Steyerberg EW, et al.
Ann Intern Med. 2007;146(6):397-405
DOI: [10.7326/0003-4819-146-6-200703200-00004](https://doi.org/10.7326/0003-4819-146-6-200703200-00004)

## Worked example

### GCS 15 and all flags false

Given: `age=30, anticoagulant_therapy=false, clinical_signs_skull_fracture=false, ejected_from_vehicle=false, fall_from_any_elevation=false, gcs=15, gcs_deterioration_1=false, gcs_deterioration_ge_2=false, loss_of_consciousness=false, neurologic_deficit=false, pedestrian_or_cyclist_vs_vehicle=false, persistent_anterograde_amnesia=false, posttraumatic_seizure=false, pta_2_to_lt_4h=false, pta_ge_4h=false, skull_contusion=false, vomiting=false`

1. GCS 15 is not a major criterion; age 30 is neither ≥60 nor the 40-60 y minor band
2. All major and minor flags are false (0 major, 0 minor)
3. CT is not indicated by the simple rule


### One major (vomiting)

Given: `age=30, anticoagulant_therapy=false, clinical_signs_skull_fracture=false, ejected_from_vehicle=false, fall_from_any_elevation=false, gcs=15, gcs_deterioration_1=false, gcs_deterioration_ge_2=false, loss_of_consciousness=false, neurologic_deficit=false, pedestrian_or_cyclist_vs_vehicle=false, persistent_anterograde_amnesia=false, posttraumatic_seizure=false, pta_2_to_lt_4h=false, pta_ge_4h=false, skull_contusion=false, vomiting=true`

1. Vomiting is a major criterion
2. CT is indicated (≥1 major)


### Two minors without a major

Given: `age=30, anticoagulant_therapy=false, clinical_signs_skull_fracture=false, ejected_from_vehicle=false, fall_from_any_elevation=true, gcs=15, gcs_deterioration_1=false, gcs_deterioration_ge_2=false, loss_of_consciousness=true, neurologic_deficit=false, pedestrian_or_cyclist_vs_vehicle=false, persistent_anterograde_amnesia=false, posttraumatic_seizure=false, pta_2_to_lt_4h=false, pta_ge_4h=false, skull_contusion=false, vomiting=false`

1. No major criterion
2. Fall from any elevation and loss of consciousness are two minor criteria
3. CT is indicated (≥2 minor)


## Also searched as

- CHIP
- CHIP prediction rule
- CT in Head Injury Patients
- Smits 2007 CHIP
- CHIP head CT rule
- simple CHIP rule
- CHIP major minor criteria
- Smits CHIP

## Parameters

- `age` (integer, required): Age in years (integer 16-120). Age ≥60 is a major criterion. Age 40-59 is the 40-60 y minor band; 39 is neither. The published rule is for patients ≥16 years.
- `gcs` (integer, required): Glasgow Coma Scale integer 13-15 as published. GCS 13 or 14 (GCS <15) is a major criterion; 15 is not. magent does not assign GCS from an exam.
- `pedestrian_or_cyclist_vs_vehicle` (boolean, required): Pedestrian or cyclist versus vehicle (Smits 2007 major). true or false as assigned by the caller. magent does not classify mechanism.
- `ejected_from_vehicle` (boolean, required): Ejected from vehicle (Smits 2007 major). true or false as assigned by the caller. magent does not classify mechanism.
- `vomiting` (boolean, required): Vomiting (Smits 2007 major). true or false as assigned by the caller. magent does not take a vomit count.
- `pta_ge_4h` (boolean, required): Posttraumatic amnesia ≥4 hours (Smits 2007 major). true or false as assigned by the caller. Mutually exclusive with pta_2_to_lt_4h. magent does not measure amnesia duration.
- `clinical_signs_skull_fracture` (boolean, required): Clinical signs of skull fracture (Smits 2007 major): any injury that suggests a skull fracture, such as palpable discontinuity of the skull, leakage of cerebrospinal fluid, raccoon-eye bruising, and bleeding from the ear, as assigned by the caller. true or false. magent does not examine the patient.
- `gcs_deterioration_ge_2` (boolean, required): GCS deterioration ≥2 points 1 hour after presentation (Smits 2007 major). true or false as assigned by the caller. Mutually exclusive with gcs_deterioration_1. magent does not assign GCS change.
- `anticoagulant_therapy` (boolean, required): Use of anticoagulant therapy (Smits 2007 major). true or false as assigned by the caller. This is the 2007 simple rule, not the 2022 CHIP update. magent does not interpret a coagulation assay.
- `posttraumatic_seizure` (boolean, required): Posttraumatic seizure (Smits 2007 major). true or false as assigned by the caller. magent does not witness a seizure.
- `fall_from_any_elevation` (boolean, required): Fall from any elevation (Smits 2007 minor). true or false as assigned by the caller. magent does not classify mechanism.
- `persistent_anterograde_amnesia` (boolean, required): Persistent anterograde amnesia, any deficit of short-term memory (Smits 2007 minor). true or false as assigned by the caller. magent does not test memory.
- `pta_2_to_lt_4h` (boolean, required): Posttraumatic amnesia of 2 to <4 hours (Smits 2007 minor). true or false as assigned by the caller. Mutually exclusive with pta_ge_4h. magent does not measure amnesia duration.
- `skull_contusion` (boolean, required): Contusion of the skull (Smits 2007 minor). true or false as assigned by the caller. magent does not examine the scalp.
- `neurologic_deficit` (boolean, required): Neurologic deficit (Smits 2007 minor). true or false as assigned by the caller. magent does not examine the patient.
- `loss_of_consciousness` (boolean, required): Loss of consciousness (Smits 2007 minor). true or false as assigned by the caller. magent does not take a history.
- `gcs_deterioration_1` (boolean, required): GCS deterioration of 1 point 1 hour after presentation (Smits 2007 minor). true or false as assigned by the caller. Mutually exclusive with gcs_deterioration_ge_2. magent does not assign GCS change.

## 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/chip`
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": [
    {
      "age": "30",
      "anticoagulant_therapy": "false",
      "clinical_signs_skull_fracture": "false",
      "ejected_from_vehicle": "false",
      "fall_from_any_elevation": "false",
      "gcs": "15",
      "gcs_deterioration_1": "false",
      "gcs_deterioration_ge_2": "false",
      "loss_of_consciousness": "false",
      "neurologic_deficit": "false",
      "pedestrian_or_cyclist_vs_vehicle": "false",
      "persistent_anterograde_amnesia": "false",
      "posttraumatic_seizure": "false",
      "pta_2_to_lt_4h": "false",
      "pta_ge_4h": "false",
      "skull_contusion": "false",
      "vomiting": "false"
    },
    {
      "age": "30",
      "anticoagulant_therapy": "false",
      "clinical_signs_skull_fracture": "false",
      "ejected_from_vehicle": "false",
      "fall_from_any_elevation": "false",
      "gcs": "15",
      "gcs_deterioration_1": "false",
      "gcs_deterioration_ge_2": "false",
      "loss_of_consciousness": "false",
      "neurologic_deficit": "false",
      "pedestrian_or_cyclist_vs_vehicle": "false",
      "persistent_anterograde_amnesia": "false",
      "posttraumatic_seizure": "false",
      "pta_2_to_lt_4h": "false",
      "pta_ge_4h": "false",
      "skull_contusion": "false",
      "vomiting": "false"
    }
  ]
}
```

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

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/chip",
  "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": "Smits M, Dippel DW, Steyerberg EW, et al.",
        "doi": "10.7326/0003-4819-146-6-200703200-00004",
        "id": "smits-2007",
        "pmid": "17371884",
        "source": "Ann Intern Med. 2007;146(6):397-405",
        "title": "Predicting intracranial traumatic findings on computed tomography in patients with minor head injury: the CHIP prediction rule"
      },
      "formula": "chip",
      "formula_expression": "ct indicated if ≥1 major (pedestrian_or_cyclist_vs_vehicle, ejected_from_vehicle, vomiting, pta_ge_4h, clinical_signs_skull_fracture, gcs < 15, gcs_deterioration_ge_2, anticoagulant_therapy, posttraumatic_seizure, age ≥ 60) or ≥2 minor (fall_from_any_elevation, persistent_anterograde_amnesia, pta_2_to_lt_4h, skull_contusion, neurologic_deficit, loss_of_consciousness, gcs_deterioration_1, age 40-60)",
      "age_years": 30,
      "criteria": [
        {
          "factor": "pedestrian_or_cyclist_vs_vehicle",
          "met": false
        },
        {
          "factor": "ejected_from_vehicle",
          "met": false
        },
        {
          "factor": "vomiting",
          "met": false
        },
        {
          "factor": "pta_ge_4h",
          "met": false
        },
        {
          "factor": "clinical_signs_skull_fracture",
          "met": false
        },
        {
          "value": 15,
          "factor": "gcs_lt_15",
          "met": false
        },
        {
          "factor": "gcs_deterioration_ge_2",
          "met": false
        },
        {
          "factor": "anticoagulant_therapy",
          "met": false
        },
        {
          "factor": "posttraumatic_seizure",
          "met": false
        },
        {
          "value": 30,
          "factor": "age_ge_60",
          "met": false
        },
        {
          "factor": "fall_from_any_elevation",
          "met": false
        },
        {
          "factor": "persistent_anterograde_amnesia",
          "met": false
        },
        {
          "factor": "pta_2_to_lt_4h",
          "met": false
        },
        {
          "factor": "skull_contusion",
          "met": false
        },
        {
          "factor": "neurologic_deficit",
          "met": false
        },
        {
          "factor": "loss_of_consciousness",
          "met": false
        },
        {
          "factor": "gcs_deterioration_1",
          "met": false
        },
        {
          "value": 30,
          "factor": "age_40_to_60",
          "met": false
        }
      ],
      "major_count": 0,
      "minor_count": 0,
      "ct_indicated": false,
      "gcs": 15
    },
    {
      "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": "Smits M, Dippel DW, Steyerberg EW, et al.",
        "doi": "10.7326/0003-4819-146-6-200703200-00004",
        "id": "smits-2007",
        "pmid": "17371884",
        "source": "Ann Intern Med. 2007;146(6):397-405",
        "title": "Predicting intracranial traumatic findings on computed tomography in patients with minor head injury: the CHIP prediction rule"
      },
      "formula": "chip",
      "formula_expression": "ct indicated if ≥1 major (pedestrian_or_cyclist_vs_vehicle, ejected_from_vehicle, vomiting, pta_ge_4h, clinical_signs_skull_fracture, gcs < 15, gcs_deterioration_ge_2, anticoagulant_therapy, posttraumatic_seizure, age ≥ 60) or ≥2 minor (fall_from_any_elevation, persistent_anterograde_amnesia, pta_2_to_lt_4h, skull_contusion, neurologic_deficit, loss_of_consciousness, gcs_deterioration_1, age 40-60)",
      "age_years": 30,
      "criteria": [
        {
          "factor": "pedestrian_or_cyclist_vs_vehicle",
          "met": false
        },
        {
          "factor": "ejected_from_vehicle",
          "met": false
        },
        {
          "factor": "vomiting",
          "met": false
        },
        {
          "factor": "pta_ge_4h",
          "met": false
        },
        {
          "factor": "clinical_signs_skull_fracture",
          "met": false
        },
        {
          "value": 15,
          "factor": "gcs_lt_15",
          "met": false
        },
        {
          "factor": "gcs_deterioration_ge_2",
          "met": false
        },
        {
          "factor": "anticoagulant_therapy",
          "met": false
        },
        {
          "factor": "posttraumatic_seizure",
          "met": false
        },
        {
          "value": 30,
          "factor": "age_ge_60",
          "met": false
        },
        {
          "factor": "fall_from_any_elevation",
          "met": false
        },
        {
          "factor": "persistent_anterograde_amnesia",
          "met": false
        },
        {
          "factor": "pta_2_to_lt_4h",
          "met": false
        },
        {
          "factor": "skull_contusion",
          "met": false
        },
        {
          "factor": "neurologic_deficit",
          "met": false
        },
        {
          "factor": "loss_of_consciousness",
          "met": false
        },
        {
          "factor": "gcs_deterioration_1",
          "met": false
        },
        {
          "value": 30,
          "factor": "age_40_to_60",
          "met": false
        }
      ],
      "major_count": 0,
      "minor_count": 0,
      "ct_indicated": false,
      "gcs": 15
    }
  ]
}
```

## Response fields

- `formula` (string): chip
- `formula_expression` (string): Smits 2007 simple CHIP rule: CT if ≥1 major or ≥2 minor
- `ct_indicated` (boolean): true when ≥1 major criterion or ≥2 minor criteria are met (Smits 2007 simple rule). Not a diagnosis and not a CT order.
- `major_count` (integer): Count of major criteria met (0-10)
- `minor_count` (integer): Count of minor criteria met (0-8)
- `gcs` (integer): GCS integer used for the GCS <15 major criterion
- `age_years` (integer): Age used for the ≥60 major and 40-60 y minor bands
- `criteria` (array): Per-factor rows with factor and met; gcs_lt_15 includes value (gcs); age_ge_60 and age_40_to_60 include value (age_years)
- `citation` (object): Smits 2007 Ann Intern Med 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": "Smits M, Dippel DW, Steyerberg EW, et al.",
    "doi": "10.7326/0003-4819-146-6-200703200-00004",
    "id": "smits-2007",
    "pmid": "17371884",
    "source": "Ann Intern Med. 2007;146(6):397-405",
    "title": "Predicting intracranial traumatic findings on computed tomography in patients with minor head injury: the CHIP prediction rule"
  },
  "formula": "chip",
  "formula_expression": "ct indicated if ≥1 major (pedestrian_or_cyclist_vs_vehicle, ejected_from_vehicle, vomiting, pta_ge_4h, clinical_signs_skull_fracture, gcs < 15, gcs_deterioration_ge_2, anticoagulant_therapy, posttraumatic_seizure, age ≥ 60) or ≥2 minor (fall_from_any_elevation, persistent_anterograde_amnesia, pta_2_to_lt_4h, skull_contusion, neurologic_deficit, loss_of_consciousness, gcs_deterioration_1, age 40-60)",
  "age_years": 30,
  "criteria": [
    {
      "factor": "pedestrian_or_cyclist_vs_vehicle",
      "met": false
    },
    {
      "factor": "ejected_from_vehicle",
      "met": false
    },
    {
      "factor": "vomiting",
      "met": false
    },
    {
      "factor": "pta_ge_4h",
      "met": false
    },
    {
      "factor": "clinical_signs_skull_fracture",
      "met": false
    },
    {
      "value": 15,
      "factor": "gcs_lt_15",
      "met": false
    },
    {
      "factor": "gcs_deterioration_ge_2",
      "met": false
    },
    {
      "factor": "anticoagulant_therapy",
      "met": false
    },
    {
      "factor": "posttraumatic_seizure",
      "met": false
    },
    {
      "value": 30,
      "factor": "age_ge_60",
      "met": false
    },
    {
      "factor": "fall_from_any_elevation",
      "met": false
    },
    {
      "factor": "persistent_anterograde_amnesia",
      "met": false
    },
    {
      "factor": "pta_2_to_lt_4h",
      "met": false
    },
    {
      "factor": "skull_contusion",
      "met": false
    },
    {
      "factor": "neurologic_deficit",
      "met": false
    },
    {
      "factor": "loss_of_consciousness",
      "met": false
    },
    {
      "factor": "gcs_deterioration_1",
      "met": false
    },
    {
      "value": 30,
      "factor": "age_40_to_60",
      "met": false
    }
  ],
  "major_count": 0,
  "minor_count": 0,
  "ct_indicated": false,
  "gcs": 15
}
```

## Errors

- HTTP 400 `invalid_chip`: CHIP inputs must match Smits 2007 simple major/minor criteria from that paper only. 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

- [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.
- [NEXUS Head CT](https://magentlab.com/docs/nexus-head-ct) — Apply the Mower 2017 NEXUS Head CT eight-criterion decision instrument and return whether the patient is low-risk (all eight caller-assigned criteria absent). CT may be omitted by this instrument when low-risk. Does not order a CT.
- [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.

## 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. HTTP 402 never includes the tool JSON.
- 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.