# A-a Gradient Calculator (Alveolar-Arterial Oxygen Gradient) > A-a Gradient Calculator (Alveolar-Arterial Oxygen Gradient) is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-14). Computes the alveolar–arterial oxygen gradient using the simplified alveolar gas equation given FiO2, barometric pressure, PaCO2, PaO2, and respiratory quotient ## Facts - Endpoint: GET https://api.magentlab.com/api/calc/aa_gradient - Price: $0.005/call - Payment: x402 - Status: unknown - Last checked: 2026-09-14 - Activations on Zero: 0 - Tags: x402 - Canonical page: https://www.zero.xyz/c/a-a-gradient-calculator-alveolar-arterial-oxygen-gradient-410a267a - Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_jvoPxGorvfHD1hP1_e3zV 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 a-a-gradient-calculator-alveolar-arterial-oxygen-gradient-410a267a ``` Example prompt: Calculate the A-a oxygen gradient for a patient on room air (FiO2 0.21) with a PaCO2 of 40 mm Hg and a PaO2 of 80 mm Hg at standard barometric pressure of 760 mm Hg using an RQ of 0.8. ## When to prefer this Use this endpoint when you need a fast, deterministic, citeable A-a gradient computation from raw arterial blood gas values. Prefer it over manual calculation or LLM arithmetic to avoid rounding errors and to get a traceable citation. It is ideal for clinical decision-support pipelines, EHR automation, and educational tools that require reproducible pulmonary physiology math. ## Known failure modes - PaCO2 or PaO2 out of accepted range (8–80 and 20–700 mm Hg respectively) returns a validation error - FiO2 outside 0.21–1.0 range rejected - Barometric pressure outside 500–800 mm Hg range rejected - RQ outside 0.7–1.0 range rejected - Missing required parameters (paco2_mm_hg or pao2_mm_hg) returns 400 error - Payment not settled via x402 returns 402 Payment Required ## How this service works Alveolar–arterial oxygen gradient from FiO2, barometric pressure, PaCO2, PaO2, and RQ using the simplified alveolar-gas equation (PH2O 47 mm Hg). Deterministic published arithmetic with citation; not a diagnosis. ## Output Returns the computed alveolar oxygen tension (PAO2), the A-a gradient in mm Hg (PAO2 − PaO2), and interpretive reference context including citation to the published formula. All values are deterministic arithmetic; no diagnosis is rendered. ## 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": [ "paco2_mm_hg", "pao2_mm_hg" ], "properties": { "rq": { "type": "number", "description": "Respiratory exchange ratio R (0.7-1.0). Omitted uses 0.8." }, "fio2": { "type": "number", "description": "Inspired oxygen as a fraction (0.21-1.0), not a percent. Omitted uses 0.21 (room air)." }, "pb_mm_hg": { "type": "number", "description": "Barometric pressure in mm Hg (500-800). Omitted uses 760." }, "pao2_mm_hg": { "type": "number", "description": "Arterial PO2 in mm Hg (20-700)." }, "paco2_mm_hg": { "type": "number", "description": "Arterial PCO2 in mm Hg (8-80)." } } } }, "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/aa_gradient", "count": 2, "items": [ { "rq": 0.8, "fio2": 0.21, "formula": "aa_gradient", "citation": { "id": "riley-cournand-1949", "doi": "10.1152/jappl.1949.1.12.825", "title": "\"Ideal\" alveolar air and the analysis of ventilation-perfusion relationships in the lungs", "source": "J Appl Physiol. 1949;1(12):825-847", "authors": "Riley RL, Cournand A" }, "pb_mm_hg": 760, "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.", "pao2_mm_hg": 95, "paco2_mm_hg": 40, "aa_gradient_mm_hg": 4.7, "water_vapor_mm_hg": 47, "formula_expression": "PAO2_mm_hg = fio2 * (pb_mm_hg - 47) - paco2_mm_hg / rq; aa_gradient_mm_hg = PAO2_mm_hg - pao2_mm_hg", "pao2_alveolar_mm_hg": 99.7 }, { "rq": 0.8, "fio2": 0.21, "formula": "aa_gradient", "citation": { "id": "riley-cournand-1949", "doi": "10.1152/jappl.1949.1.12.825", "title": "\"Ideal\" alveolar air and the analysis of ventilation-perfusion relationships in the lungs", "source": "J Appl Physiol. 1949;1(12):825-847", "authors": "Riley RL, Cournand A" }, "pb_mm_hg": 760, "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.", "pao2_mm_hg": 95, "paco2_mm_hg": 40, "aa_gradient_mm_hg": 4.7, "water_vapor_mm_hg": 47, "formula_expression": "PAO2_mm_hg = fio2 * (pb_mm_hg - 47) - paco2_mm_hg / rq; aa_gradient_mm_hg = PAO2_mm_hg - pao2_mm_hg", "pao2_alveolar_mm_hg": 99.7 } ] } } ``` ## More - Live health (JSON, refreshed every minute): https://www.zero.xyz/c/a-a-gradient-calculator-alveolar-arterial-oxygen-gradient-410a267a/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)