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magent S/F Ratio Calculator
x402
magent S/F Ratio 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 SpO2/FiO2 (S/F) ratio by dividing pulse-oximetry SpO2 percentage by inspired oxygen fraction, returning the ratio rounded to one decimal place.
Price / call$0.005
Success—
StatusUnknown
How this service works
SpO2/FiO2 (S/F) ratio as pulse-oximetry SpO2 percent divided by inspired oxygen as a fraction (0.21–1.0) (Rice 2007). Returns the ratio rounded to one decimal. Magent does not apply ARDS or Berlin bands. This is not the PaO2/FiO2 (P/F) ratio and not the ROX index.
Output
Returns a single numeric S/F ratio (SpO2% ÷ FiO2 fraction) rounded to one decimal place. This is the Rice 2007 surrogate oxygenation index — not the P/F ratio and not the ROX index.
Example use cases
ICU respiratory failure triage
“My ICU patient has an SpO2 of 88% and is on high-flow oxygen with FiO2 of 0.60 — what is their S/F ratio?”
Non-invasive ARDS screening
“Can you compute the S/F ratio for a patient with SpO2 of 96% breathing room air (FiO2 0.21)? We want to assess oxygenation without an arterial blood gas.”
Serial oxygenation trending
“Track the S/F ratio for a patient whose SpO2 improved from 90% to 95% on FiO2 0.50 — calculate the new ratio so we can compare to the earlier value.”
Technical details
Endpoint
GEThttps://api.magentlab.com/api/calc/sf_ratioWhen to prefer
Choose this endpoint when you need a fast, non-invasive oxygenation index and arterial blood gas (PaO2) is unavailable or impractical — i.e., when you have pulse-oximetry SpO2 but not a measured PaO2. Use the sibling PaO2/FiO2 endpoint instead when arterial blood gas values are available. Do not use this for ROX index (which incorporates respiratory rate) or for formal ARDS/Berlin criteria banding.
Side effects
- FiO2 outside 0.21–1.0 range returns validation error
- SpO2 outside 50–100% range returns validation error
- Missing required query parameters returns 400 error
- Payment not provided or declined returns 402 error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"path": "/api/calc/sf_ratio",
"count": 2,
"items": [
{
"fio2": 0.21,
"formula": "sf_ratio",
"citation": {
"id": "rice-2007",
"doi": "10.1378/chest.07-0617",
"title": "Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS",
"source": "Chest. 2007;132(2):410-417",
"authors": "Rice TW, Wheeler AP, Bernard GR, Hayden DL, Schoenfeld DA, Ware LB"
},
"sf_ratio": 452.4,
"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.",
"spo2_percent": 95,
"formula_expression": "sf_ratio = spo2_percent / fio2"
},
{
"fio2": 0.21,
"formula": "sf_ratio",
"citation": {
"id": "rice-2007",
"doi": "10.1378/chest.07-0617",
"title": "Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS",
"source": "Chest. 2007;132(2):410-417",
"authors": "Rice TW, Wheeler AP, Bernard GR, Hayden DL, Schoenfeld DA, Ware LB"
},
"sf_ratio": 452.4,
"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.",
"spo2_percent": 95,
"formula_expression": "sf_ratio = spo2_percent / fio2"
}
]
}
}Tags
x402
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