# Leiden undifferentiated arthritis prediction rule Leiden UA rule Status: LIVE Price: $0.005 USDC `GET /api/calc/leiden_arthritis` HTML: https://magentlab.com/docs/leiden-arthritis Markdown: https://magentlab.com/docs/leiden-arthritis.md Not a medical device. Not a diagnosis, dose, or listing recommendation. ## What it computes Sum the van der Helm-van Mil 2007 simplified Leiden prediction score for recent-onset undifferentiated arthritis and return the paper’s ≤6 / 6–8 / ≥8 decision band. ## When to use When an agent already has age, sex, caller-assigned joint-distribution flags, 100-mm morning-stiffness VAS, tender and swollen joint counts, CRP in mg/L, and RF/anti-CCP flags and needs the published Leiden UA score, not an RA diagnosis. ## When not to use - Not a medical device and not a diagnosis of rheumatoid arthritis or a treatment order. - magent does not examine joints or assay serologies. Age, sex, distribution flags, 100-mm VAS, joint counts, CRP, RF, and anti-CCP are caller-assigned. - Morning stiffness is the published 100-mm VAS severity, not duration in minutes. - If upper_and_lower_extremities is true, the 1-point upper_extremities row is ignored (1.5 only). Small-joint and symmetric rows may stack with that extremity row. - The total is rounded to the nearest number ending in .0 or .5 (paper Table 3). Bands are the paper decision cutoffs: ≤6 low, >6 and <8 indeterminate, ≥8 high. max_score 14. Not a classification of RA. ## Formula ``` Leiden UA score (van der Helm-van Mil 2007 Figure 1 / Table 2) = age_years*0.02 + female 1 + small_joints_hands_feet 0.5 + symmetric 0.5 + (upper_and_lower_extremities 1.5 else upper_extremities 1) + morning_stiffness_vas_mm (0–25 → 0; 26–90 → 1; >90 → 2) + tender_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + swollen_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + crp_mg_l (0–4 → 0; 5–50 → 0.5; ≥51 → 1.5) + rheumatoid_factor_positive 1 + anti_ccp_positive 2; round to nearest 0.0 or 0.5; ≤6 low, >6 and <8 indeterminate, ≥8 high; max 14; not a diagnosis of RA ``` ## Citation [A prediction rule for disease outcome in patients with recent-onset undifferentiated arthritis: how to guide individual treatment decisions](https://doi.org/10.1002/art.22380) van der Helm-van Mil AH, le Cessie S, van Dongen H, Breedveld FC, Toes RE, Huizinga TW Arthritis Rheum. 2007;56(2):433-440 DOI: [10.1002/art.22380](https://doi.org/10.1002/art.22380) ## Worked example ### Age 48 female, RF negative: 7.46 rounds to 7.5 indeterminate Given: `age=48, anti_ccp_positive=false, crp_mg_l=60, morning_stiffness_vas_mm=50, rheumatoid_factor_positive=false, sex=female, small_joints_hands_feet=true, swollen_joint_count=8, symmetric=true, tender_joint_count=8, upper_and_lower_extremities=false, upper_extremities=true` 1. age 48 × 0.02 = 0.96; female 1; small joints 0.5; symmetric 0.5; upper extremities 1; VAS 50 → 1; tender 8 → 0.5; swollen 8 → 0.5; CRP 60 → 1.5; RF 0; anti-CCP 0 2. unrounded 7.46; round to nearest 0.0 or 0.5 → 7.5; leiden_band indeterminate (>6 and <8) ### Same inputs with RF positive: 8.46 rounds to 8.5 high Given: `age=48, anti_ccp_positive=false, crp_mg_l=60, morning_stiffness_vas_mm=50, rheumatoid_factor_positive=true, sex=female, small_joints_hands_feet=true, swollen_joint_count=8, symmetric=true, tender_joint_count=8, upper_and_lower_extremities=false, upper_extremities=true` 1. prior unrounded 7.46 + RF 1 = 8.46 2. round to nearest 0.0 or 0.5 → 8.5; leiden_band high (≥8) ### Score 6.0 is low Given: `age=50, anti_ccp_positive=false, crp_mg_l=0, morning_stiffness_vas_mm=50, rheumatoid_factor_positive=false, sex=female, small_joints_hands_feet=true, swollen_joint_count=8, symmetric=true, tender_joint_count=8, upper_and_lower_extremities=false, upper_extremities=true` 1. age 50 × 0.02 = 1; female 1; small 0.5; symmetric 0.5; upper 1; VAS 50 → 1; tender 8 → 0.5; swollen 8 → 0.5; CRP 0; RF 0; anti-CCP 0 2. score = 6.0 (≤6); leiden_band low ## Also searched as - Leiden prediction rule - Leiden UA rule - undifferentiated arthritis score - van der Helm-van Mil 2007 - early arthritis prediction rule - Leiden RA prediction score ## Parameters - `age` (integer, required): Age in years as an integer from 18 to 120 (van der Helm-van Mil 2007). Scores age_years × 0.02. magent does not assign age. - `sex` (string, required): Caller-assigned sex (van der Helm-van Mil 2007). female scores 1; male scores 0. magent does not assign sex. - `small_joints_hands_feet` (boolean, required): Involvement of small joints of the hands or feet (van der Helm-van Mil 2007). true scores 0.5 and may stack with symmetric and the extremity row. magent does not examine joints. - `symmetric` (boolean, required): Symmetric joint involvement (van der Helm-van Mil 2007). true scores 0.5 and may stack with small-joint and extremity rows. magent does not examine joints. - `upper_extremities` (boolean, required): Involvement of upper extremities only (van der Helm-van Mil 2007). true scores 1 unless upper_and_lower_extremities is true, in which case this row is ignored. Mutually exclusive with the 1.5 upper-and-lower row. magent does not examine joints. - `upper_and_lower_extremities` (boolean, required): Involvement of upper and lower extremities (van der Helm-van Mil 2007). true scores 1.5 and ignores upper_extremities. magent does not examine joints. - `morning_stiffness_vas_mm` (number, required): Morning-stiffness severity on a 100-mm VAS (van der Helm-van Mil 2007), not duration in minutes. Number 0–100. 0–25 scores 0; 26–90 scores 1; >90 scores 2. magent does not take a history. - `tender_joint_count` (integer, required): Caller-assigned tender joint count (van der Helm-van Mil 2007). Integer 0–68. <4 scores 0; 4–10 scores 0.5; ≥11 scores 1. magent does not examine joints. - `swollen_joint_count` (integer, required): Caller-assigned swollen joint count (van der Helm-van Mil 2007). Integer 0–66. <4 scores 0; 4–10 scores 0.5; ≥11 scores 1. magent does not examine joints. - `crp_mg_l` (number, required): Caller-assigned C-reactive protein in mg/L (van der Helm-van Mil 2007). Number 0–500. 0–4 scores 0; 5–50 scores 0.5; ≥51 scores 1.5. magent does not assay CRP. - `rheumatoid_factor_positive` (boolean, required): Caller-assigned rheumatoid factor positivity (van der Helm-van Mil 2007). true scores 1. magent does not assay serologies. - `anti_ccp_positive` (boolean, required): Caller-assigned anti-CCP (ACPA) positivity (van der Helm-van Mil 2007). true scores 2. magent does not assay serologies. ## 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/leiden_arthritis` 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": "48", "anti_ccp_positive": "false", "crp_mg_l": "60", "morning_stiffness_vas_mm": "50", "rheumatoid_factor_positive": "false", "sex": "female", "small_joints_hands_feet": "true", "swollen_joint_count": "8", "symmetric": "true", "tender_joint_count": "8", "upper_and_lower_extremities": "false", "upper_extremities": "true" }, { "age": "48", "anti_ccp_positive": "false", "crp_mg_l": "60", "morning_stiffness_vas_mm": "50", "rheumatoid_factor_positive": "false", "sex": "female", "small_joints_hands_feet": "true", "swollen_joint_count": "8", "symmetric": "true", "tender_joint_count": "8", "upper_and_lower_extremities": "false", "upper_extremities": "true" } ] } ``` Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/leiden-arthritis Example 200: ```json { "count": 2, "path": "/api/calc/leiden_arthritis", "items": [ { "components": [ { "value": 48, "factor": "age", "points": 0.96, "present": true }, { "value": "female", "factor": "female", "points": 1, "present": true }, { "factor": "small_joints_hands_feet", "points": 0.5, "present": true }, { "factor": "symmetric", "points": 0.5, "present": true }, { "factor": "upper_and_lower_extremities", "points": 0.0, "present": false }, { "factor": "upper_extremities", "points": 1.0, "present": true }, { "value": 50.0, "factor": "morning_stiffness_vas_mm", "points": 1, "present": true }, { "value": 8, "factor": "tender_joint_count", "points": 0.5, "present": true }, { "value": 8, "factor": "swollen_joint_count", "points": 0.5, "present": true }, { "value": 60.0, "factor": "crp_mg_l", "points": 1.5, "present": true }, { "factor": "rheumatoid_factor_positive", "points": 0, "present": false }, { "factor": "anti_ccp_positive", "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 der Helm-van Mil AH, le Cessie S, van Dongen H, Breedveld FC, Toes RE, Huizinga TW", "doi": "10.1002/art.22380", "id": "van-der-helm-van-mil-2007", "pmid": "17265478", "source": "Arthritis Rheum. 2007;56(2):433-440", "title": "A prediction rule for disease outcome in patients with recent-onset undifferentiated arthritis: how to guide individual treatment decisions" }, "formula": "leiden_arthritis", "formula_expression": "Leiden UA score (van der Helm-van Mil 2007 Figure 1 / Table 2) = age_years*0.02 + female 1 + small_joints_hands_feet 0.5 + symmetric 0.5 + (upper_and_lower_extremities 1.5 else upper_extremities 1) + morning_stiffness_vas_mm (0–25 → 0; 26–90 → 1; >90 → 2) + tender_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + swollen_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + crp_mg_l (0–4 → 0; 5–50 → 0.5; ≥51 → 1.5) + rheumatoid_factor_positive 1 + anti_ccp_positive 2; round to nearest 0.0 or 0.5; ≤6 low, >6 and <8 indeterminate, ≥8 high; max 14; not a diagnosis of RA", "max_score": 14, "score": 7.5, "leiden_band": "indeterminate" }, { "components": [ { "value": 48, "factor": "age", "points": 0.96, "present": true }, { "value": "female", "factor": "female", "points": 1, "present": true }, { "factor": "small_joints_hands_feet", "points": 0.5, "present": true }, { "factor": "symmetric", "points": 0.5, "present": true }, { "factor": "upper_and_lower_extremities", "points": 0.0, "present": false }, { "factor": "upper_extremities", "points": 1.0, "present": true }, { "value": 50.0, "factor": "morning_stiffness_vas_mm", "points": 1, "present": true }, { "value": 8, "factor": "tender_joint_count", "points": 0.5, "present": true }, { "value": 8, "factor": "swollen_joint_count", "points": 0.5, "present": true }, { "value": 60.0, "factor": "crp_mg_l", "points": 1.5, "present": true }, { "factor": "rheumatoid_factor_positive", "points": 0, "present": false }, { "factor": "anti_ccp_positive", "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 der Helm-van Mil AH, le Cessie S, van Dongen H, Breedveld FC, Toes RE, Huizinga TW", "doi": "10.1002/art.22380", "id": "van-der-helm-van-mil-2007", "pmid": "17265478", "source": "Arthritis Rheum. 2007;56(2):433-440", "title": "A prediction rule for disease outcome in patients with recent-onset undifferentiated arthritis: how to guide individual treatment decisions" }, "formula": "leiden_arthritis", "formula_expression": "Leiden UA score (van der Helm-van Mil 2007 Figure 1 / Table 2) = age_years*0.02 + female 1 + small_joints_hands_feet 0.5 + symmetric 0.5 + (upper_and_lower_extremities 1.5 else upper_extremities 1) + morning_stiffness_vas_mm (0–25 → 0; 26–90 → 1; >90 → 2) + tender_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + swollen_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + crp_mg_l (0–4 → 0; 5–50 → 0.5; ≥51 → 1.5) + rheumatoid_factor_positive 1 + anti_ccp_positive 2; round to nearest 0.0 or 0.5; ≤6 low, >6 and <8 indeterminate, ≥8 high; max 14; not a diagnosis of RA", "max_score": 14, "score": 7.5, "leiden_band": "indeterminate" } ] } ``` ## Response fields - `formula` (string): leiden_arthritis - `formula_expression` (string): Exact expression used - `score` (number): van der Helm-van Mil 2007 simplified prediction score rounded to the nearest 0.0 or 0.5 (Table 3 grouping). Half-points allowed. - `max_score` (integer): 14 - `leiden_band` (string): Paper decision cutoffs on the rounded score: low (≤6), indeterminate (>6 and <8), or high (≥8). Not a diagnosis of RA. - `components` (array): Per-factor points before rounding - `citation` (object): van der Helm-van Mil et al. Arthritis Rheum 2007 citation - `disclaimer` (string): Not-a-device notice ## Example JSON Frozen fixture. Not a live lookup. ```json { "components": [ { "value": 48, "factor": "age", "points": 0.96, "present": true }, { "value": "female", "factor": "female", "points": 1, "present": true }, { "factor": "small_joints_hands_feet", "points": 0.5, "present": true }, { "factor": "symmetric", "points": 0.5, "present": true }, { "factor": "upper_and_lower_extremities", "points": 0.0, "present": false }, { "factor": "upper_extremities", "points": 1.0, "present": true }, { "value": 50.0, "factor": "morning_stiffness_vas_mm", "points": 1, "present": true }, { "value": 8, "factor": "tender_joint_count", "points": 0.5, "present": true }, { "value": 8, "factor": "swollen_joint_count", "points": 0.5, "present": true }, { "value": 60.0, "factor": "crp_mg_l", "points": 1.5, "present": true }, { "factor": "rheumatoid_factor_positive", "points": 0, "present": false }, { "factor": "anti_ccp_positive", "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 der Helm-van Mil AH, le Cessie S, van Dongen H, Breedveld FC, Toes RE, Huizinga TW", "doi": "10.1002/art.22380", "id": "van-der-helm-van-mil-2007", "pmid": "17265478", "source": "Arthritis Rheum. 2007;56(2):433-440", "title": "A prediction rule for disease outcome in patients with recent-onset undifferentiated arthritis: how to guide individual treatment decisions" }, "formula": "leiden_arthritis", "formula_expression": "Leiden UA score (van der Helm-van Mil 2007 Figure 1 / Table 2) = age_years*0.02 + female 1 + small_joints_hands_feet 0.5 + symmetric 0.5 + (upper_and_lower_extremities 1.5 else upper_extremities 1) + morning_stiffness_vas_mm (0–25 → 0; 26–90 → 1; >90 → 2) + tender_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + swollen_joint_count (<4 → 0; 4–10 → 0.5; ≥11 → 1) + crp_mg_l (0–4 → 0; 5–50 → 0.5; ≥51 → 1.5) + rheumatoid_factor_positive 1 + anti_ccp_positive 2; round to nearest 0.0 or 0.5; ≤6 low, >6 and <8 indeterminate, ≥8 high; max 14; not a diagnosis of RA", "max_score": 14, "score": 7.5, "leiden_band": "indeterminate" } ``` ## Errors - HTTP 400 `invalid_age`: age must be an integer from 18 to 120 Returned before settlement; you are not charged. - HTTP 400 `invalid_sex`: sex must be female or male Returned before settlement; you are not charged. - HTTP 400 `invalid_leiden`: morning_stiffness_vas_mm must be 0–100; tender_joint_count an integer 0–68; swollen_joint_count an integer 0–66; crp_mg_l a number 0–500 (van der Helm-van Mil 2007 Leiden UA rule). 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 - [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. - [SDAI](https://magentlab.com/docs/sdai) — Sum caller-assigned 28-joint swollen and tender counts, 0–10 cm patient and evaluator globals, and CRP in mg/dL, and return the Aletaha 2005 SDAI with the newly proposed activity state. - [ACR/EULAR PMR](https://magentlab.com/docs/acr-eular-pmr) — Apply the 2012 EULAR/ACR polymyalgia rheumatica classification criteria (Dasgupta Table 4): require age ≥50, bilateral shoulder aching, and abnormal CRP and/or ESR, then return the clinical score with or without optional ultrasound and whether the published cut point classifies PMR. Not a PMR 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.