# San Francisco Syncope Rule (CHESS Score) Calculator > San Francisco Syncope Rule (CHESS Score) Calculator 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). Calculates the San Francisco Syncope Rule (CHESS) score from five clinical criteria to identify high-risk syncope patients, returning a criterion count (0–5) and rule-positive flag. ## Facts - Endpoint: GET https://api.magentlab.com/api/calc/sf_syncope - 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/san-francisco-syncope-rule-chess-score-calculator-6d17621c - Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_zAvAHcng30bivgxwcmNeo 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 san-francisco-syncope-rule-chess-score-calculator-6d17621c ``` Example prompt: Score this syncope patient on the San Francisco Syncope Rule: they have a history of CHF, hematocrit is 27%, ECG is abnormal, no shortness of breath, and systolic BP is 105 mm Hg. ## When to prefer this Use this endpoint when you need a deterministic, citation-backed implementation of the San Francisco Syncope Rule (CHESS) for syncope risk stratification — particularly when building clinical decision support workflows, automating chart review, or auditing ED syncope management. Prefer this over general-purpose LLM reasoning for medical scoring because it guarantees adherence to the published Elesber/Quinn algorithm with traceable citation, not probabilistic generation. It is not a disposition protocol and should be used alongside clinical judgment. ## Known failure modes - Missing required query parameters (chf, hematocrit_percent, abnormal_ecg, shortness_of_breath, systolic_bp_mm_hg) returns a validation error - Hematocrit value outside accepted range (10–70%) returns an out-of-range error - Systolic BP value outside accepted range (50–250 mm Hg) returns an out-of-range error - Non-boolean values passed for boolean parameters return a type error - Payment not included or insufficient USDC triggers a 402 Payment Required response ## How this service works San Francisco Syncope Rule (CHESS) from history of CHF, hematocrit, abnormal ECG, shortness of breath, and systolic BP. Returns a 0-5 criterion count and rule-positive if any CHESS item is present. Deterministic published score with citation; not a disposition protocol. ## Output Returns the total number of CHESS criteria met (integer 0–5) and a boolean rule-positive flag indicating whether any single criterion is present, which per the published rule identifies high-risk syncope. Individual criterion contributions are also available to explain which items scored positive. ## 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": [ "chf", "hematocrit_percent", "abnormal_ecg", "shortness_of_breath", "systolic_bp_mm_hg" ], "properties": { "chf": { "type": "boolean", "description": "History of congestive heart failure (C). true or false." }, "abnormal_ecg": { "type": "boolean", "description": "Abnormal ECG (E). true or false. Caller-assigned; magent does not read tracings." }, "systolic_bp_mm_hg": { "type": "number", "description": "Systolic BP in mm Hg (50-250). Scores 1 when <90; 90 is negative." }, "hematocrit_percent": { "type": "number", "description": "Hematocrit in percent (10-70). Scores 1 when <30; 30 is negative." }, "shortness_of_breath": { "type": "boolean", "description": "Shortness of breath (S). true or false." } } } }, "additionalProperties": false }, "output": { "type": "object", "required": [ "type" ], "properties": { "type": { "type": "string" }, "example": { "type": "object" } } } } } ``` ## Response schema (JSON Schema) ```json { "type": "json", "example": { "path": "/api/calc/sf_syncope", "count": 2, "items": [ { "score": 0, "formula": "sf_syncope", "citation": { "id": "quinn-2004", "doi": "10.1016/S0196-0644(03)00823-0", "title": "Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes", "source": "Ann Emerg Med. 2004;43(2):224-232", "authors": "Quinn JV, Stiell IG, McDermott DA, Sellers KL, Kohn MA, Wells GA" }, "max_score": 5, "components": [ { "factor": "chf", "points": 0, "present": false }, { "value": 40, "factor": "hematocrit_lt_30", "points": 0, "present": false }, { "factor": "abnormal_ecg", "points": 0, "present": false }, { "factor": "shortness_of_breath", "points": 0, "present": false }, { "value": 120, "factor": "systolic_bp_lt_90", "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.", "rule_positive": false, "systolic_bp_mm_hg": 120, "formula_expression": "CHESS = chf + hematocrit_lt_30 + abnormal_ecg + shortness_of_breath + systolic_bp_lt_90; rule-positive if score ≥ 1; max 5", "hematocrit_percent": 40 }, { "score": 0, "formula": "sf_syncope", "citation": { "id": "quinn-2004", "doi": "10.1016/S0196-0644(03)00823-0", "title": "Derivation of the San Francisco Syncope Rule to predict patients with short-term serious outcomes", "source": "Ann Emerg Med. 2004;43(2):224-232", "authors": "Quinn JV, Stiell IG, McDermott DA, Sellers KL, Kohn MA, Wells GA" }, "max_score": 5, "components": [ { "factor": "chf", "points": 0, "present": false }, { "value": 40, "factor": "hematocrit_lt_30", "points": 0, "present": false }, { "factor": "abnormal_ecg", "points": 0, "present": false }, { "factor": "shortness_of_breath", "points": 0, "present": false }, { "value": 120, "factor": "systolic_bp_lt_90", "points": 0, "present": false } ], "disclaimer": "Not a medical device. Deterministic published-formula or published-code … (truncated) ``` ## More - Live health (JSON, refreshed every minute): https://www.zero.xyz/c/san-francisco-syncope-rule-chess-score-calculator-6d17621c/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)