LACE index (van Walraven)

LACE

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.

LIVE $0.005 USDC GET /api/calc/lace

Markdown: /docs/lace.md · Canonical: https://magentlab.com/docs/lace

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

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

Worked example

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

Given: acute_admission=falsecharlson=0ed_visits_6mo=0length_of_stay_days=1

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

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

Given: acute_admission=truecharlson=4ed_visits_6mo=4length_of_stay_days=14

LOS 14 → 7; acute true → 3; Charlson 4 → 5; ED 4 → 4
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

Try

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

/api/calc/lace?length_of_stay_days=1&acute_admission=false&charlson=0&ed_visits_6mo=0

Full URL: https://api.magentlab.com/api/calc/lace?length_of_stay_days=1&acute_admission=false&charlson=0&ed_visits_6mo=0

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/lace?length_of_stay_days=1&acute_admission=false&charlson=0&ed_visits_6mo=0"

Parameters

Name	Type	Required	Description
`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.

POST /api/calc/lace Max 25 unit_amount + extra_item_amount * (n - 1) extra $0.002 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 (fixture)

{
  "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"
    }
  ]
}

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/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

Field	Type	Description
`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

Machine form of the same example. Frozen fixture. Not a live lookup.

{
  "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
}

Client errors (HTTP 400)

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

HTTP	Code	When
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.
400	`invalid_flag`	boolean clinical flags must be true or false Returned before settlement; you are not charged.
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.
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.
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

RCRI — Sum the six Lee 1999 revised cardiac risk index factors and return class I–IV.
San Francisco Syncope Rule — 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. 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

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.