# Leiden Arthritis Prediction Rule Calculator (van der Helm-van Mil 2007) > Leiden Arthritis Prediction Rule Calculator (van der Helm-van Mil 2007) is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-15). Computes the van der Helm-van Mil 2007 Leiden prediction rule score for recent-onset undifferentiated arthritis to stratify risk of RA development into low, indeterminate, or high bands. ## Facts - Endpoint: GET https://api.magentlab.com/api/calc/leiden_arthritis - Price: $0.005/call - Payment: x402 - Status: unknown - Last checked: 2026-09-15 - Activations on Zero: 0 - Tags: x402 - Canonical page: https://www.zero.xyz/c/leiden-arthritis-prediction-rule-calculator-van-der-helm-van-mil-2007-a656f6c8 - Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_I-jNHjnKYEf6nlqttEhgK Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently. ## How to call it through Zero Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`): ```sh zero fetch --capability leiden-arthritis-prediction-rule-calculator-van-der-helm-van-mil-2007-a656f6c8 ``` Example prompt: Apply the van der Helm-van Mil 2007 Leiden prediction rule for this patient: 52-year-old female, small joints of hands and feet involved, symmetric, upper extremities only, morning stiffness VAS 70 mm, 5 tender joints, 3 swollen joints, CRP 18 mg/L, rheumatoid factor positive, anti-CCP negative — what's her RA risk band? ## When to prefer this Use this endpoint when you need a fast, reproducible implementation of the van der Helm-van Mil 2007 Leiden prediction rule specifically for recent-onset undifferentiated arthritis risk stratification. Prefer it over general clinical calculators when the exact published scoring weights and band thresholds (≤6 low, >6–<8 indeterminate, ≥8 high) are required. Not appropriate for established RA diagnosis, pediatric patients, or other arthritis prediction rules. ## Known failure modes - Missing required query parameter returns an error (all 12 parameters are required) - Out-of-range age (e.g. below 18 or above 120) may cause validation failure - Invalid enum value for sex (must be 'female' or 'male') causes rejection - Non-boolean values for boolean fields cause schema validation errors - CRP values outside 0–500 mg/L range may not be handled gracefully - Conflicting extremity flags (both upper_extremities and upper_and_lower_extremities true) may produce unexpected scores — upper_and_lower takes precedence ## How this service works van der Helm-van Mil 2007 Leiden prediction rule for recent-onset undifferentiated arthritis (Figure 1 / Table 2). Age × 0.02, female 1, small joints 0.5, symmetric 0.5, upper 1 or upper-and-lower 1.5, 100-mm morning-stiffness VAS 0/1/2, tender and swollen counts 0/0.5/1, CRP mg/L 0/0.5/1.5, RF 1, anti-CCP 2. Round to nearest 0.0 or 0.5. Bands ≤6 low, >6 and <8 indeterminate, ≥8 high. Not a diagnosis of RA. magent does not examine joints or assay serologies. ## Output Returns the computed Leiden prediction rule total score (rounded to nearest 0.0 or 0.5) and a risk band classification: ≤6 = low, >6 and <8 = indeterminate, ≥8 = high. This is a risk stratification tool, not a diagnosis of rheumatoid arthritis. ## Request schema (JSON Schema) ```json { "type": "object", "$schema": "https://json-schema.org/draft/2020-12/schema", "required": [ "input" ], "properties": { "input": { "type": "object", "required": [ "type", "method" ], "properties": { "type": { "type": "string", "const": "http" }, "method": { "enum": [ "GET", "HEAD", "DELETE" ], "type": "string" }, "headers": { "type": "object", "additionalProperties": { "type": "string" } }, "queryParams": { "type": "object", "required": [ "age", "sex", "small_joints_hands_feet", "symmetric", "upper_extremities", "upper_and_lower_extremities", "morning_stiffness_vas_mm", "tender_joint_count", "swollen_joint_count", "crp_mg_l", "rheumatoid_factor_positive", "anti_ccp_positive" ], "properties": { "age": { "type": "integer", "description": "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": { "enum": [ "female", "male" ], "type": "string", "description": "Caller-assigned sex (van der Helm-van Mil 2007). female scores 1; male scores 0. magent does not assign sex." }, "crp_mg_l": { "type": "number", "description": "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." }, "symmetric": { "type": "boolean", "description": "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." }, "anti_ccp_positive": { "type": "boolean", "description": "Caller-assigned anti-CCP (ACPA) positivity (van der Helm-van Mil 2007). true scores 2. magent does not assay serologies." }, "upper_extremities": { "type": "boolean", "description": "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." }, "tender_joint_count": { "type": "integer", "description": "Caller-assigned tender joint count (van der Helm- … (truncated) ``` ## More - Live health (JSON, refreshed every minute): https://www.zero.xyz/c/leiden-arthritis-prediction-rule-calculator-van-der-helm-van-mil-2007-a656f6c8/health.json - [Zero catalog index](https://www.zero.xyz/llms.txt) - [Other services from api.magentlab.com](https://www.zero.xyz/host/api.magentlab.com/llms.txt)