# LACE index (van Walraven)

LACE

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

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

## What it computes

Sum van Walraven 2010 Table 3 LACE points from length of stay, acute (emergent) admission, a caller-supplied Charlson integer, and ED visits in the previous 6 months.

## When to use

When an agent needs the published Table 3 LACE total (0–19) and must not invent a ≥10 high-risk class or treat the score as a discharge order.

## When not to use

- Not a medical device and not a discharge, admission, or follow-up order. magent does not examine the patient.
- Does not compute the Charlson comorbidity index. The caller supplies the integer Charlson score (0–37); magent maps that integer to Table 3 points only.
- Table 3 returns a 0–19 point total only. magent does not invent a ≥10 high-risk class; that cutoff is later practice, not named classes in van Walraven 2010.

## Formula

```
LACE = los_points + acute_admission_points + charlson_points + ed_visits_points; van Walraven 2010 Table 3; LOS <1 0, 1 1, 2 2, 3 3, 4-6 4, 7-13 5, >=14 7; acute true 3; Charlson 0-3 identity, >=4 5; ED 0-3 identity, >=4 4; max 19
```

## Citation

[Derivation and validation of an index to predict early death or unplanned readmission after discharge from hospital to the community](https://doi.org/10.1503/cmaj.091117)
van Walraven C, Dhalla IA, Bell C, Etchells E, Stiell IG, Zarnke K, Austin PC, Forster AJ
CMAJ. 2010;182(6):551-557
DOI: [10.1503/cmaj.091117](https://doi.org/10.1503/cmaj.091117)

## Worked example

### LOS 1 day, elective, Charlson 0, no ED visits

Given: `acute_admission=false, charlson=0, ed_visits_6mo=0, length_of_stay_days=1`

1. LOS 1 → 1; acute false → 0; Charlson 0 → 0; ED 0 → 0
2. Score = 1 (max 19)


### Table 3 maximum (LOS ≥14, acute, Charlson ≥4, ED ≥4)

Given: `acute_admission=true, charlson=4, ed_visits_6mo=4, length_of_stay_days=14`

1. LOS 14 → 7; acute true → 3; Charlson 4 → 5; ED 4 → 4
2. Score = 19 (max 19). Table 3 total only; not a named high-risk class.


## Also searched as

- LACE index
- LACE score
- van Walraven LACE
- length of stay acute Charlson ED
- hospital readmission index
- LACE readmission

## Parameters

- `length_of_stay_days` (integer, required): Length of stay in days (integer 0-365). van Walraven 2010 Table 3 L: <1 → 0, 1 → 1, 2 → 2, 3 → 3, 4-6 → 4, 7-13 → 5, ≥14 → 7. 0 days is the <1 bin.
- `acute_admission` (boolean, required): Acute (emergent) admission as assigned by the caller (true or false). van Walraven 2010 Table 3 A: true → 3, false → 0.
- `charlson` (integer, required): Caller-supplied Charlson comorbidity index (integer 0-37). magent does not compute Charlson. van Walraven 2010 Table 3 C: 0 → 0, 1 → 1, 2 → 2, 3 → 3, ≥4 → 5.
- `ed_visits_6mo` (integer, required): Emergency-department visits in the previous 6 months (integer 0-30). van Walraven 2010 Table 3 E: 0 → 0, 1 → 1, 2 → 2, 3 → 3, ≥4 → 4.

## 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/lace`
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": [
    {
      "acute_admission": "false",
      "charlson": "0",
      "ed_visits_6mo": "0",
      "length_of_stay_days": "1"
    },
    {
      "acute_admission": "false",
      "charlson": "0",
      "ed_visits_6mo": "0",
      "length_of_stay_days": "1"
    }
  ]
}
```

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

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/lace",
  "items": [
    {
      "components": [
        {
          "value": 1,
          "factor": "length_of_stay",
          "points": 1,
          "present": true
        },
        {
          "factor": "acute_admission",
          "points": 0,
          "present": false
        },
        {
          "value": 0,
          "factor": "charlson",
          "points": 0,
          "present": false
        },
        {
          "value": 0,
          "factor": "ed_visits_6mo",
          "points": 0,
          "present": 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": "van Walraven C, Dhalla IA, Bell C, Etchells E, Stiell IG, Zarnke K, Austin PC, Forster AJ",
        "doi": "10.1503/cmaj.091117",
        "id": "van-walraven-2010",
        "pmid": "20194559",
        "source": "CMAJ. 2010;182(6):551-557",
        "title": "Derivation and validation of an index to predict early death or unplanned readmission after discharge from hospital to the community"
      },
      "formula": "lace",
      "formula_expression": "LACE = los_points + acute_admission_points + charlson_points + ed_visits_points; van Walraven 2010 Table 3; LOS <1 0, 1 1, 2 2, 3 3, 4-6 4, 7-13 5, >=14 7; acute true 3; Charlson 0-3 identity, >=4 5; ED 0-3 identity, >=4 4; max 19",
      "max_score": 19,
      "score": 1,
      "acute_admission": false,
      "charlson": 0,
      "ed_visits_6mo": 0,
      "length_of_stay_days": 1
    },
    {
      "components": [
        {
          "value": 1,
          "factor": "length_of_stay",
          "points": 1,
          "present": true
        },
        {
          "factor": "acute_admission",
          "points": 0,
          "present": false
        },
        {
          "value": 0,
          "factor": "charlson",
          "points": 0,
          "present": false
        },
        {
          "value": 0,
          "factor": "ed_visits_6mo",
          "points": 0,
          "present": 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": "van Walraven C, Dhalla IA, Bell C, Etchells E, Stiell IG, Zarnke K, Austin PC, Forster AJ",
        "doi": "10.1503/cmaj.091117",
        "id": "van-walraven-2010",
        "pmid": "20194559",
        "source": "CMAJ. 2010;182(6):551-557",
        "title": "Derivation and validation of an index to predict early death or unplanned readmission after discharge from hospital to the community"
      },
      "formula": "lace",
      "formula_expression": "LACE = los_points + acute_admission_points + charlson_points + ed_visits_points; van Walraven 2010 Table 3; LOS <1 0, 1 1, 2 2, 3 3, 4-6 4, 7-13 5, >=14 7; acute true 3; Charlson 0-3 identity, >=4 5; ED 0-3 identity, >=4 4; max 19",
      "max_score": 19,
      "score": 1,
      "acute_admission": false,
      "charlson": 0,
      "ed_visits_6mo": 0,
      "length_of_stay_days": 1
    }
  ]
}
```

## Response fields

- `formula` (string): lace
- `formula_expression` (string): Exact expression used
- `score` (integer): LACE points 0-19 (Table 3 only)
- `max_score` (integer): Always 19
- `length_of_stay_days` (integer): Length of stay in days used for Table 3 L
- `acute_admission` (boolean): Acute (emergent) admission flag used for Table 3 A
- `charlson` (integer): Caller-supplied Charlson integer used for Table 3 C
- `ed_visits_6mo` (integer): ED visits in the previous 6 months used for Table 3 E
- `components` (array): Per-letter Table 3 points
- `citation` (object): van Walraven et al. CMAJ 2010 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "components": [
    {
      "value": 1,
      "factor": "length_of_stay",
      "points": 1,
      "present": true
    },
    {
      "factor": "acute_admission",
      "points": 0,
      "present": false
    },
    {
      "value": 0,
      "factor": "charlson",
      "points": 0,
      "present": false
    },
    {
      "value": 0,
      "factor": "ed_visits_6mo",
      "points": 0,
      "present": 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": "van Walraven C, Dhalla IA, Bell C, Etchells E, Stiell IG, Zarnke K, Austin PC, Forster AJ",
    "doi": "10.1503/cmaj.091117",
    "id": "van-walraven-2010",
    "pmid": "20194559",
    "source": "CMAJ. 2010;182(6):551-557",
    "title": "Derivation and validation of an index to predict early death or unplanned readmission after discharge from hospital to the community"
  },
  "formula": "lace",
  "formula_expression": "LACE = los_points + acute_admission_points + charlson_points + ed_visits_points; van Walraven 2010 Table 3; LOS <1 0, 1 1, 2 2, 3 3, 4-6 4, 7-13 5, >=14 7; acute true 3; Charlson 0-3 identity, >=4 5; ED 0-3 identity, >=4 4; max 19",
  "max_score": 19,
  "score": 1,
  "acute_admission": false,
  "charlson": 0,
  "ed_visits_6mo": 0,
  "length_of_stay_days": 1
}
```

## Errors

- HTTP 400 `invalid_length_of_stay`: length_of_stay_days must be an integer from 0 to 365 (van Walraven 2010 LACE). Returned before settlement; you are not charged.
- HTTP 400 `invalid_flag`: boolean clinical flags must be true or false Returned before settlement; you are not charged.
- HTTP 400 `invalid_charlson`: charlson must be an integer from 0 to 37 (van Walraven 2010 LACE uses the Charlson score as input). Returned before settlement; you are not charged.
- HTTP 400 `invalid_ed_visits`: ed_visits_6mo must be an integer from 0 to 30 (van Walraven 2010 LACE). 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

- [RCRI](https://magentlab.com/docs/rcri) — Sum the six Lee 1999 revised cardiac risk index factors and return class I–IV.
- [San Francisco Syncope Rule](https://magentlab.com/docs/sf-syncope) — Compute the San Francisco Syncope Rule (CHESS) criterion count and rule-positive flag from published cutoffs.

## 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.