# ASAS peripheral SpA classification criteria

ASAS peripheral SpA

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/asas_peripheral_spa`
HTML: https://magentlab.com/docs/asas-peripheral-spa
Markdown: https://magentlab.com/docs/asas-peripheral-spa.md

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

## What it computes

Apply the 2011 ASAS classification criteria for peripheral spondyloarthritis (Rudwaleit set 2D / figure 1): require current arthritis, enthesitis, or dactylitis, then return whether arm A (≥1 of 6 SpA features) or arm B (≥2 of 5 additional features) classifies peripheral SpA. Not a diagnosis.

## When to use

When an agent already has caller-assigned Rudwaleit 2011 entry and SpA feature flags and needs the published peripheral SpA classification result for research, not a diagnosis, not ASAS 2009 axial, and not ESSG/Amor.

## When not to use

- Not a medical device and not a diagnosis of peripheral spondyloarthritis, psoriatic arthritis, reactive arthritis, or IBD-associated SpA. Classification criteria for research.
- Entry (current arthritis, enthesitis, or dactylitis) must be met or the request is HTTP 400 and is not returned as classified=false.
- Age at onset is a study limitation (Rudwaleit 2011 usually ≤45 years) and is not a parameter and not an HTTP 400.
- This tool is ASAS 2011 peripheral SpA classification (set 2D) only. It is not the 2009 ASAS axial criteria and not ESSG or Amor criteria.
- Arthritis, enthesitis, dactylitis, psoriasis, IBD, preceding infection, HLA-B27, uveitis, sacroiliitis on imaging, IBP in the past, and family history are caller-assigned. magent does not examine joints or assay HLA-B27.

## Formula

```
ASAS 2011 peripheral SpA classification (Rudwaleit set 2D / fig 1 + table 5): required arthritis or enthesitis or dactylitis (current). arm_a iff ≥1 of psoriasis, ibd, preceding_infection, hla_b27, uveitis, sacroiliitis_on_imaging. arm_b iff ≥2 of arthritis, enthesitis, dactylitis, ibp_past, family_history_spa (same caller flags as entry for arthritis/enthesitis/dactylitis). classified iff entry and (arm_a or arm_b). Not a diagnosis. Not ASAS 2009 axial. Not ESSG/Amor
```

## Citation

[The Assessment of SpondyloArthritis international Society classification criteria for peripheral spondyloarthritis and for spondyloarthritis in general](https://doi.org/10.1136/ard.2010.133645)
Rudwaleit M, van der Heijde D, Landewé R, Akkoc N, Brandt J, Chou CT, Dougados M, Huang F, Gu J, Kirazli Y, Van den Bosch F, Olivieri I, Roussou E, Scarpato S, Sørensen IJ, Valle-Oñate R, Weber U, Wei J, Sieper J
Ann Rheum Dis. 2011;70(1):25-31
DOI: [10.1136/ard.2010.133645](https://doi.org/10.1136/ard.2010.133645)

## Worked example

### Arthritis plus psoriasis, arm A

Given: `arthritis=true, dactylitis=false, enthesitis=false, family_history_spa=false, hla_b27=false, ibd=false, ibp_past=false, preceding_infection=false, psoriasis=true, sacroiliitis_on_imaging=false, uveitis=false`

1. Required: arthritis true (entry met); enthesitis and dactylitis false
2. psoriasis true; remaining arm A flags false → arm_a_count 1, arm_a true
3. arm_b_count 1 (arthritis only of 5); arm_b false; classified true


### Arthritis plus enthesitis, arm B

Given: `arthritis=true, dactylitis=false, enthesitis=true, family_history_spa=false, hla_b27=false, ibd=false, ibp_past=false, preceding_infection=false, psoriasis=false, sacroiliitis_on_imaging=false, uveitis=false`

1. arthritis and enthesitis true; no arm A features
2. arm_a_count 0; arm_b_count 2
3. arm_a false; arm_b true; classified true


### Entry met, one arm B feature, not classified

Given: `arthritis=true, dactylitis=false, enthesitis=false, family_history_spa=false, hla_b27=false, ibd=false, ibp_past=false, preceding_infection=false, psoriasis=false, sacroiliitis_on_imaging=false, uveitis=false`

1. arthritis true; remaining flags false
2. arm_a_count 0; arm_b_count 1
3. arm_a false; arm_b false; classified false


### Arthritis plus HLA-B27, arm A

Given: `arthritis=true, dactylitis=false, enthesitis=false, family_history_spa=false, hla_b27=true, ibd=false, ibp_past=false, preceding_infection=false, psoriasis=false, sacroiliitis_on_imaging=false, uveitis=false`

1. arthritis true; hla_b27 true; remaining flags false
2. arm_a_count 1; arm_b_count 1
3. arm_a true; arm_b false; classified true


### Arthritis plus sacroiliitis on imaging, arm A

Given: `arthritis=true, dactylitis=false, enthesitis=false, family_history_spa=false, hla_b27=false, ibd=false, ibp_past=false, preceding_infection=false, psoriasis=false, sacroiliitis_on_imaging=true, uveitis=false`

1. arthritis true; sacroiliitis_on_imaging true; remaining flags false
2. arm_a_count 1; arm_b_count 1
3. arm_a true; arm_b false; classified true


## Also searched as

- ASAS peripheral spondyloarthritis
- ASAS 2011 classification criteria
- Rudwaleit peripheral SpA
- peripheral spondyloarthritis classification
- ASAS pSpA
- not ASAS 2009 axial
- not ESSG Amor criteria
- HLA-B27 peripheral SpA

## Parameters

- `arthritis` (boolean, required): Current peripheral arthritis (usually asymmetric and/or of lower limbs) as assigned by the caller (Rudwaleit 2011 set 2D entry). Table 5 additional feature is past or present synovitis diagnosed by a physician; the same caller flag counts toward arm B. true or false. magent does not examine joints.
- `enthesitis` (boolean, required): Current enthesitis as assigned by the caller (Rudwaleit 2011 set 2D entry). Table 5 additional feature is past or present spontaneous pain or tenderness at an enthesis; the same caller flag counts toward arm B. true or false. magent does not examine entheses.
- `dactylitis` (boolean, required): Current dactylitis as assigned by the caller (Rudwaleit 2011 set 2D entry). Table 5 additional feature is past or present dactylitis diagnosed by a physician; the same caller flag counts toward arm B. true or false. magent does not examine digits.
- `psoriasis` (boolean, required): Past or present psoriasis diagnosed by a physician, as assigned by the caller (Rudwaleit 2011 arm A). true or false. magent does not examine skin.
- `ibd` (boolean, required): Past or present Crohn's disease or ulcerative colitis diagnosed by a physician, as assigned by the caller (Rudwaleit 2011 arm A). true or false. magent does not diagnose IBD.
- `preceding_infection` (boolean, required): Urethritis/cervicitis or diarrhoea within 1 month before arthritis, enthesitis, or dactylitis, as assigned by the caller (Rudwaleit 2011 arm A). true or false. magent does not take a history.
- `hla_b27` (boolean, required): HLA-B27 positive as assigned by the caller (Rudwaleit 2011 arm A). true or false. magent does not assay HLA-B27.
- `uveitis` (boolean, required): Past or present uveitis confirmed by an ophthalmologist, as assigned by the caller (Rudwaleit 2011 arm A). true or false. magent does not examine the eye.
- `sacroiliitis_on_imaging` (boolean, required): Sacroiliitis on imaging as assigned by the caller (Rudwaleit 2011 arm A): definite radiographic sacroiliitis (bilateral grade 2–4 or unilateral grade 3–4) or active inflammation on MRI highly suggestive of SpA-associated sacroiliitis. true or false. magent does not read films.
- `ibp_past` (boolean, required): Inflammatory back pain in the past according to experts, as assigned by the caller (Rudwaleit 2011 arm B). true or false. magent does not take a history.
- `family_history_spa` (boolean, required): Family history of SpA as assigned by the caller (Rudwaleit 2011 arm B): first-degree or second-degree relatives with ankylosing spondylitis, psoriasis, acute uveitis, reactive arthritis, or IBD. true or false. magent does not take a pedigree.

## 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/asas_peripheral_spa`
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": [
    {
      "arthritis": "true",
      "dactylitis": "false",
      "enthesitis": "false",
      "family_history_spa": "false",
      "hla_b27": "false",
      "ibd": "false",
      "ibp_past": "false",
      "preceding_infection": "false",
      "psoriasis": "true",
      "sacroiliitis_on_imaging": "false",
      "uveitis": "false"
    },
    {
      "arthritis": "true",
      "dactylitis": "false",
      "enthesitis": "false",
      "family_history_spa": "false",
      "hla_b27": "false",
      "ibd": "false",
      "ibp_past": "false",
      "preceding_infection": "false",
      "psoriasis": "true",
      "sacroiliitis_on_imaging": "false",
      "uveitis": "false"
    }
  ]
}
```

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

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/asas_peripheral_spa",
  "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": "Rudwaleit M, van der Heijde D, Landewé R, Akkoc N, Brandt J, Chou CT, Dougados M, Huang F, Gu J, Kirazli Y, Van den Bosch F, Olivieri I, Roussou E, Scarpato S, Sørensen IJ, Valle-Oñate R, Weber U, Wei J, Sieper J",
        "doi": "10.1136/ard.2010.133645",
        "id": "rudwaleit-2011",
        "pmid": "21109520",
        "source": "Ann Rheum Dis. 2011;70(1):25-31",
        "title": "The Assessment of SpondyloArthritis international Society classification criteria for peripheral spondyloarthritis and for spondyloarthritis in general"
      },
      "formula": "asas_peripheral_spa",
      "formula_expression": "ASAS 2011 peripheral SpA classification (Rudwaleit set 2D / fig 1 + table 5): required arthritis or enthesitis or dactylitis (current). arm_a iff ≥1 of psoriasis, ibd, preceding_infection, hla_b27, uveitis, sacroiliitis_on_imaging. arm_b iff ≥2 of arthritis, enthesitis, dactylitis, ibp_past, family_history_spa (same caller flags as entry for arthritis/enthesitis/dactylitis). classified iff entry and (arm_a or arm_b). Not a diagnosis. Not ASAS 2009 axial. Not ESSG/Amor",
      "classified": true,
      "arm_a": true,
      "arm_a_count": 1,
      "arm_b": false,
      "arm_b_count": 1
    },
    {
      "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": "Rudwaleit M, van der Heijde D, Landewé R, Akkoc N, Brandt J, Chou CT, Dougados M, Huang F, Gu J, Kirazli Y, Van den Bosch F, Olivieri I, Roussou E, Scarpato S, Sørensen IJ, Valle-Oñate R, Weber U, Wei J, Sieper J",
        "doi": "10.1136/ard.2010.133645",
        "id": "rudwaleit-2011",
        "pmid": "21109520",
        "source": "Ann Rheum Dis. 2011;70(1):25-31",
        "title": "The Assessment of SpondyloArthritis international Society classification criteria for peripheral spondyloarthritis and for spondyloarthritis in general"
      },
      "formula": "asas_peripheral_spa",
      "formula_expression": "ASAS 2011 peripheral SpA classification (Rudwaleit set 2D / fig 1 + table 5): required arthritis or enthesitis or dactylitis (current). arm_a iff ≥1 of psoriasis, ibd, preceding_infection, hla_b27, uveitis, sacroiliitis_on_imaging. arm_b iff ≥2 of arthritis, enthesitis, dactylitis, ibp_past, family_history_spa (same caller flags as entry for arthritis/enthesitis/dactylitis). classified iff entry and (arm_a or arm_b). Not a diagnosis. Not ASAS 2009 axial. Not ESSG/Amor",
      "classified": true,
      "arm_a": true,
      "arm_a_count": 1,
      "arm_b": false,
      "arm_b_count": 1
    }
  ]
}
```

## Response fields

- `formula` (string): asas_peripheral_spa
- `formula_expression` (string): Rudwaleit 2011 ASAS peripheral SpA classification expression (set 2D / fig 1)
- `classified` (boolean): true iff arm_a or arm_b after required current arthritis, enthesitis, or dactylitis. Classification criteria for research, not a diagnosis of peripheral SpA. Not ASAS 2009 axial. Not ESSG/Amor.
- `arm_a` (boolean): true iff ≥1 of psoriasis, ibd, preceding_infection, hla_b27, uveitis, sacroiliitis_on_imaging (Rudwaleit 2011 fig 1)
- `arm_b` (boolean): true iff ≥2 of arthritis, enthesitis, dactylitis, ibp_past, family_history_spa (Rudwaleit 2011 fig 1). Arthritis, enthesitis, and dactylitis use the same caller flags as entry.
- `arm_a_count` (integer): Count of the 6 arm A SpA features that are true (0–6).
- `arm_b_count` (integer): Count of the 5 arm B additional features that are true (0–5), including arthritis, enthesitis, and dactylitis when true.
- `citation` (object): Rudwaleit 2011 Ann Rheum Dis 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": "Rudwaleit M, van der Heijde D, Landewé R, Akkoc N, Brandt J, Chou CT, Dougados M, Huang F, Gu J, Kirazli Y, Van den Bosch F, Olivieri I, Roussou E, Scarpato S, Sørensen IJ, Valle-Oñate R, Weber U, Wei J, Sieper J",
    "doi": "10.1136/ard.2010.133645",
    "id": "rudwaleit-2011",
    "pmid": "21109520",
    "source": "Ann Rheum Dis. 2011;70(1):25-31",
    "title": "The Assessment of SpondyloArthritis international Society classification criteria for peripheral spondyloarthritis and for spondyloarthritis in general"
  },
  "formula": "asas_peripheral_spa",
  "formula_expression": "ASAS 2011 peripheral SpA classification (Rudwaleit set 2D / fig 1 + table 5): required arthritis or enthesitis or dactylitis (current). arm_a iff ≥1 of psoriasis, ibd, preceding_infection, hla_b27, uveitis, sacroiliitis_on_imaging. arm_b iff ≥2 of arthritis, enthesitis, dactylitis, ibp_past, family_history_spa (same caller flags as entry for arthritis/enthesitis/dactylitis). classified iff entry and (arm_a or arm_b). Not a diagnosis. Not ASAS 2009 axial. Not ESSG/Amor",
  "classified": true,
  "arm_a": true,
  "arm_a_count": 1,
  "arm_b": false,
  "arm_b_count": 1
}
```

## Errors

- HTTP 400 `invalid_asas_peripheral`: arthritis, enthesitis, or dactylitis must be true (Rudwaleit 2011 ASAS peripheral SpA set 2D entry: current peripheral arthritis, enthesitis, or dactylitis). 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_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

- [ASAS axial SpA](https://magentlab.com/docs/asas-axial-spa) — Apply the 2009 ASAS classification criteria for axial spondyloarthritis (Rudwaleit set 3a / figure 2): require chronic back pain ≥3 months with age at onset <45, then return whether the imaging arm (sacroiliitis plus ≥1 SpA feature) or the clinical arm (HLA-B27 plus ≥2 other SpA features) classifies axial SpA. Not a diagnosis.
- [ACR/EULAR gout](https://magentlab.com/docs/acr-eular-gout) — Apply the 2015 ACR/EULAR gout classification criteria (Neogi Table 2): require the entry episode, classify immediately if MSU crystals are present, otherwise return the Step 3 score (max 23) and whether score ≥8 classifies gout. Not a gout diagnosis.
- [ACR/EULAR Sjögren](https://magentlab.com/docs/acr-eular-sjogren) — Apply the 2016 ACR/EULAR classification criteria for primary Sjögren's syndrome (Shiboski Table 3): require published inclusion and no exclusion, then return the five-item weighted score and whether the ≥4 cut point classifies primary Sjögren's syndrome. Not a diagnosis.

## 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.