Electrolytes / glucose · LIVE

CPR index (C-peptide to plasma glucose ratio)

CPR index

Compute the Saisho 2011 C-peptide-to-plasma-glucose ratio (CPR index) from serum C-peptide in ng/mL and plasma glucose in mg/dL.

LIVE $0.005 USDC GET /api/calc/cpri

Markdown: /docs/cpri.md · Canonical: https://magentlab.com/docs/cpri

Not a medical device. Not a diagnosis, dose, or listing recommendation.

What it computes

Compute the Saisho 2011 C-peptide-to-plasma-glucose ratio (CPR index) from serum C-peptide in ng/mL and plasma glucose in mg/dL.

When to use

When an agent needs the published CPR index and the 2.02 ROC cut-off flag and must not invent HOMA-IR, a diabetes diagnosis, or an insulin order.

When not to use

• Not a diabetes diagnosis, not HOMA-IR, and not C-peptide alone. Glucose is mg/dL only; magent does not convert mmol/L.
• below_best_cutoff is true only when cpri is strictly less than 2.02, the Saisho 2011 best ROC cut-off for later insulin therapy (80.8% sensitivity, 63.3% specificity). That flag is not an insulin order.
• The paper also notes a cut-off of 1.5 with about 80% specificity and 60% sensitivity; magent does not return a second flag for 1.5.
• Fasting and postprandial use the same arithmetic; timing is a required caller label, not a different formula. Not a medical device.

Formula

cpri = c_peptide_ng_ml / glucose_mg_dl * 100

Citation

Title

Postprandial serum C-peptide to plasma glucose ratio as a predictor of subsequent insulin treatment in patients with type 2 diabetes

Authors

Saisho Y, Kou K, Tanaka K, Abe T, Kurosawa H, Shimada A, Meguro S, Kawai T, Itoh H

Source

Endocr J. 2011;58(4):315-322

DOI

10.1507/endocrj.K10E-399

Worked example

Also searched as

• CPR index
• C-peptide to glucose ratio
• CPRI
• Saisho CPR index
• postprandial C-peptide glucose
• fasting C-peptide index
• serum CPR plasma glucose
• C-peptide immunoreactivity index

Try

Opens the live endpoint. Unpaid browser requests show the paywall; agents should send Accept: application/json.

/api/calc/cpri?timing=postprandial&c_peptide_ng_ml=2.02&glucose_mg_dl=100

Full URL: https://api.magentlab.com/api/calc/cpri?timing=postprandial&c_peptide_ng_ml=2.02&glucose_mg_dl=100

Call

Expect HTTP 402 until you retry with PAYMENT-SIGNATURE. Incomplete query params return HTTP 400 before any quote or charge.

curl -i -H "Accept: application/json" "https://api.magentlab.com/api/calc/cpri?timing=postprandial&c_peptide_ng_ml=2.02&glucose_mg_dl=100"

Parameters

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.

POST /api/calc/cpri Max 25 unit_amount + extra_item_amount * (n - 1) extra $0.002 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 (fixture)

{
  "items": [
    {
      "c_peptide_ng_ml": "2.02",
      "glucose_mg_dl": "100",
      "timing": "postprandial"
    },
    {
      "c_peptide_ng_ml": "2.02",
      "glucose_mg_dl": "100",
      "timing": "postprandial"
    }
  ]
}

Open bulk paywall →

Opens a two-item fixture on the API host. Unpaid browsers get the same MetaMask paywall as GET; Pay retries POST with those items.

Example 200 (fixture)

{
  "count": 2,
  "path": "/api/calc/cpri",
  "items": [
    {
      "timing": "postprandial",
      "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": "Saisho Y, Kou K, Tanaka K, Abe T, Kurosawa H, Shimada A, Meguro S, Kawai T, Itoh H",
        "doi": "10.1507/endocrj.K10E-399",
        "id": "saisho-2011",
        "pmid": "21528347",
        "source": "Endocr J. 2011;58(4):315-322",
        "title": "Postprandial serum C-peptide to plasma glucose ratio as a predictor of subsequent insulin treatment in patients with type 2 diabetes"
      },
      "formula": "cpri",
      "formula_expression": "cpri = c_peptide_ng_ml / glucose_mg_dl * 100",
      "glucose_mg_dl": 100.0,
      "below_best_cutoff": false,
      "c_peptide_ng_ml": 2.02,
      "cpri": 2.02
    },
    {
      "timing": "postprandial",
      "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": "Saisho Y, Kou K, Tanaka K, Abe T, Kurosawa H, Shimada A, Meguro S, Kawai T, Itoh H",
        "doi": "10.1507/endocrj.K10E-399",
        "id": "saisho-2011",
        "pmid": "21528347",
        "source": "Endocr J. 2011;58(4):315-322",
        "title": "Postprandial serum C-peptide to plasma glucose ratio as a predictor of subsequent insulin treatment in patients with type 2 diabetes"
      },
      "formula": "cpri",
      "formula_expression": "cpri = c_peptide_ng_ml / glucose_mg_dl * 100",
      "glucose_mg_dl": 100.0,
      "below_best_cutoff": false,
      "c_peptide_ng_ml": 2.02,
      "cpri": 2.02
    }
  ]
}

Response

Example JSON

Machine form of the same example. Frozen fixture. Not a live lookup.

{
  "timing": "postprandial",
  "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": "Saisho Y, Kou K, Tanaka K, Abe T, Kurosawa H, Shimada A, Meguro S, Kawai T, Itoh H",
    "doi": "10.1507/endocrj.K10E-399",
    "id": "saisho-2011",
    "pmid": "21528347",
    "source": "Endocr J. 2011;58(4):315-322",
    "title": "Postprandial serum C-peptide to plasma glucose ratio as a predictor of subsequent insulin treatment in patients with type 2 diabetes"
  },
  "formula": "cpri",
  "formula_expression": "cpri = c_peptide_ng_ml / glucose_mg_dl * 100",
  "glucose_mg_dl": 100.0,
  "below_best_cutoff": false,
  "c_peptide_ng_ml": 2.02,
  "cpri": 2.02
}

Client errors (HTTP 400)

Invalid params return 400 without charge. Shared HTTP 402 and 503 meanings: Payments.

Related tools

• HOMA-IR — Compute the Matthews 1985 HOMA-IR approximation from fasting plasma glucose and insulin.
• A1C ↔ eAG — Convert A1C percent to estimated average glucose, or the reverse, using Nathan/ADAG.

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. Unpaid valid requests return HTTP 402 with a base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote: retry the same PAYMENT-SIGNATURE. Full handshake and shared payment errors: Payments. Stdio MCP: /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.