# CPR index (C-peptide to plasma glucose ratio) CPR index Status: LIVE Price: $0.005 USDC `GET /api/calc/cpri` HTML: https://magentlab.com/docs/cpri Markdown: https://magentlab.com/docs/cpri.md 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 [Postprandial serum C-peptide to plasma glucose ratio as a predictor of subsequent insulin treatment in patients with type 2 diabetes](https://doi.org/10.1507/endocrj.K10E-399) Saisho Y, Kou K, Tanaka K, Abe T, Kurosawa H, Shimada A, Meguro S, Kawai T, Itoh H Endocr J. 2011;58(4):315-322 DOI: [10.1507/endocrj.K10E-399](https://doi.org/10.1507/endocrj.K10E-399) ## Worked example ### Postprandial CPR 2.02 ng/mL, glucose 100 mg/dL Given: `c_peptide_ng_ml=2.02, glucose_mg_dl=100, timing=postprandial` 1. cpri = 2.02 / 100 * 100 = 2.02 2. 2.02 is not < 2.02 → below_best_cutoff false ### Postprandial CPR 1.0 ng/mL, glucose 100 mg/dL Given: `c_peptide_ng_ml=1.0, glucose_mg_dl=100, timing=postprandial` 1. cpri = 1.0 / 100 * 100 = 1.00 2. 1.00 < 2.02 → below_best_cutoff true ### Fasting CPR 3.0 ng/mL, glucose 90 mg/dL Given: `c_peptide_ng_ml=3.0, glucose_mg_dl=90, timing=fasting` 1. cpri = 3.0 / 90 * 100 = 3.33 2. 3.33 is not < 2.02 → below_best_cutoff false ## 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 ## Parameters - `timing` (string, required): Sample timing as assigned by the caller: fasting or postprandial. Same CPR-index arithmetic; magent does not pick a formula from the clock. - `c_peptide_ng_ml` (number, required): Serum C-peptide in ng/mL (0-40). Saisho 2011 CPR units. - `glucose_mg_dl` (number, required): Plasma glucose in mg/dL (50-1000). mg/dL only; magent does not convert mmol/L. ## 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. Method: `POST /api/calc/cpri` Max items: 25 Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic) Status: 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: ```json { "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" } ] } ``` Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/cpri Example 200: ```json { "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 fields - `formula` (string): cpri - `formula_expression` (string): Exact expression used - `cpri` (number): Saisho 2011 CPR index, 2 decimals - `below_best_cutoff` (boolean): true iff cpri < 2.02 (Saisho 2011 best ROC cut-off for later insulin therapy). Not an insulin order. - `timing` (string): fasting or postprandial as supplied by the caller - `c_peptide_ng_ml` (number): Serum C-peptide in ng/mL used - `glucose_mg_dl` (number): Plasma glucose in mg/dL used - `citation` (object): Saisho et al. 2011 citation - `disclaimer` (string): Not-a-device notice ## Example JSON Frozen fixture. Not a live lookup. ```json { "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 } ``` ## Errors - HTTP 400 `invalid_c_peptide`: c_peptide_ng_ml must be a number from 0 to 40 (Saisho 2011 CPR ng/mL). Returned before settlement; you are not charged. - HTTP 400 `invalid_glucose`: glucose_mg_dl (50-1000) or glucose_mmol_l (2.8-55.5) is required Returned before settlement; you are not charged. - HTTP 400 `invalid_cpri_timing`: timing must be fasting or postprandial (Saisho 2011 CPR index). Returned before settlement; you are not charged. - HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged. - HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged. - HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged. Shared HTTP 402 and 503: https://magentlab.com/docs/payments ## Related tools - [HOMA-IR](https://magentlab.com/docs/homa-ir) — Compute the Matthews 1985 HOMA-IR approximation from fasting plasma glucose and insulin. - [A1C ↔ eAG](https://magentlab.com/docs/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. - GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall). - HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote. - Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering. - Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional. - Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402. - offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront. - offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization. - not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search. Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers). Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments Stdio MCP (one process per host): https://magentlab.com/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.