# BUN/creatinine ratio

BUN/creatinine ratio

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/bun_creatinine_ratio`
HTML: https://magentlab.com/docs/bun-creatinine-ratio
Markdown: https://magentlab.com/docs/bun-creatinine-ratio.md

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

## What it computes

Compute the Richards 1990 blood urea nitrogen to creatinine ratio and whether that ratio is >= 36 (suggests upper gastrointestinal bleeding).

## When to use

When an agent needs the published Richards 1990 BUN/creatinine ratio and must not invent a lower-GI class, an endoscopy order, or Glasgow-Blatchford urea bands.

## When not to use

- Not a medical device.
- Not a diagnosis. magent does not locate a gastrointestinal bleed and does not order endoscopy.
- A ratio >= 36 suggests upper gastrointestinal bleeding. A ratio < 36 is not helpful in locating the source; magent does not classify that as lower GI bleeding.
- Richards 1990: no patient with lower GI bleeding had a ratio >= 36; 38% of patients with upper GI bleeding had a ratio >= 36. Those figures are not returned in the JSON body.
- Not the Glasgow-Blatchford urea or BUN tables. This tool does not score Blatchford bands.

## Formula

```
bun_creatinine_ratio = bun_mg_dl / creatinine_mg_dl
```

## Citation

[Can the blood urea nitrogen/creatinine ratio distinguish upper from lower gastrointestinal bleeding?](https://doi.org/10.1097/00004836-199010000-00004)
Richards RJ, Donica MB, Grayer D
J Clin Gastroenterol. 1990;12(5):500-504
DOI: [10.1097/00004836-199010000-00004](https://doi.org/10.1097/00004836-199010000-00004)

## Worked example

### BUN 36, creatinine 1

Given: `bun_mg_dl=36, creatinine_mg_dl=1`

1. bun_creatinine_ratio = 36 / 1 = 36.0
2. 36.0 >= 36 → suggests_upper_gi_bleeding true


### BUN 35, creatinine 1

Given: `bun_mg_dl=35, creatinine_mg_dl=1`

1. bun_creatinine_ratio = 35 / 1 = 35.0
2. 35.0 is not >= 36 → suggests_upper_gi_bleeding false


## Also searched as

- BUN creatinine ratio
- BUN/Cr ratio
- blood urea nitrogen creatinine ratio
- Richards GI bleed ratio
- upper GI bleeding BUN creatinine
- BUN Cr localization
- azotemia GI bleed

## Parameters

- `bun_mg_dl` (number, required): Blood urea nitrogen in mg/dL (1-200). Richards 1990 ratio uses BUN in mg/dL. Not a Glasgow-Blatchford urea band. magent does not assay BUN.
- `creatinine_mg_dl` (number, optional): Serum creatinine in mg/dL (0.1-20). Provide this or creatinine_umol_l, not both. magent does not assay creatinine.
- `creatinine_umol_l` (number, optional): Serum creatinine in µmol/L (9-1768). Converted as mg/dL = µmol/L / 88.42. Provide this or creatinine_mg_dl, not both.

## 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/bun_creatinine_ratio`
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": [
    {
      "bun_mg_dl": "36",
      "creatinine_mg_dl": "1"
    },
    {
      "bun_mg_dl": "36",
      "creatinine_mg_dl": "1"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/bun-creatinine-ratio

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/bun_creatinine_ratio",
  "items": [
    {
      "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": "Richards RJ, Donica MB, Grayer D",
        "doi": "10.1097/00004836-199010000-00004",
        "id": "richards-1990",
        "pmid": "2229992",
        "source": "J Clin Gastroenterol. 1990;12(5):500-504",
        "title": "Can the blood urea nitrogen/creatinine ratio distinguish upper from lower gastrointestinal bleeding?"
      },
      "formula": "bun_creatinine_ratio",
      "formula_expression": "bun_creatinine_ratio = bun_mg_dl / creatinine_mg_dl",
      "creatinine_mg_dl": 1.0,
      "bun_mg_dl": 36.0,
      "bun_creatinine_ratio": 36.0,
      "suggests_upper_gi_bleeding": true
    },
    {
      "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": "Richards RJ, Donica MB, Grayer D",
        "doi": "10.1097/00004836-199010000-00004",
        "id": "richards-1990",
        "pmid": "2229992",
        "source": "J Clin Gastroenterol. 1990;12(5):500-504",
        "title": "Can the blood urea nitrogen/creatinine ratio distinguish upper from lower gastrointestinal bleeding?"
      },
      "formula": "bun_creatinine_ratio",
      "formula_expression": "bun_creatinine_ratio = bun_mg_dl / creatinine_mg_dl",
      "creatinine_mg_dl": 1.0,
      "bun_mg_dl": 36.0,
      "bun_creatinine_ratio": 36.0,
      "suggests_upper_gi_bleeding": true
    }
  ]
}
```

## Response fields

- `formula` (string): bun_creatinine_ratio
- `formula_expression` (string): Exact expression used
- `bun_mg_dl` (number): BUN used in mg/dL
- `creatinine_mg_dl` (number): Serum creatinine used in mg/dL (after conversion)
- `bun_creatinine_ratio` (number): BUN divided by creatinine in mg/dL, 1 decimal
- `suggests_upper_gi_bleeding` (boolean): true when bun_creatinine_ratio is >= 36 after 1-decimal rounding
- `citation` (object): Richards 1990 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "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": "Richards RJ, Donica MB, Grayer D",
    "doi": "10.1097/00004836-199010000-00004",
    "id": "richards-1990",
    "pmid": "2229992",
    "source": "J Clin Gastroenterol. 1990;12(5):500-504",
    "title": "Can the blood urea nitrogen/creatinine ratio distinguish upper from lower gastrointestinal bleeding?"
  },
  "formula": "bun_creatinine_ratio",
  "formula_expression": "bun_creatinine_ratio = bun_mg_dl / creatinine_mg_dl",
  "creatinine_mg_dl": 1.0,
  "bun_mg_dl": 36.0,
  "bun_creatinine_ratio": 36.0,
  "suggests_upper_gi_bleeding": true
}
```

## Errors

- HTTP 400 `invalid_bun`: bun_mg_dl must be a number from 1 to 200. Returned before settlement; you are not charged.
- HTTP 400 `invalid_creatinine`: creatinine_mg_dl (0.1-20) or creatinine_umol_l (9-1768) is required 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

- [Glasgow-Blatchford score](https://magentlab.com/docs/glasgow-blatchford) — Compute the Blatchford 2000 Glasgow-Blatchford score from urea, haemoglobin, systolic BP, heart rate, and four clinical flags.
- [Oakland score](https://magentlab.com/docs/oakland) — Sum the Oakland 2017 derivation-table weights for acute lower gastrointestinal bleeding and return safe_discharge (score ≤8) or not_safe (score >8).
- [Rockall](https://magentlab.com/docs/rockall) — Compute the Rockall 1996 complete (post-endoscopy) score from age, heart rate, systolic blood pressure, caller-assigned comorbidity, diagnosis, and stigmata of recent haemorrhage after acute upper gastrointestinal haemorrhage.

## 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.