# Urine anion gap

Urine anion gap

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/urine_anion_gap`
HTML: https://magentlab.com/docs/urine-anion-gap
Markdown: https://magentlab.com/docs/urine-anion-gap.md

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

## What it computes

Compute the urine anion gap from urine sodium, potassium, and chloride as a surrogate for ammonium excretion in hyperchloremic metabolic acidosis.

## When to use

When an agent needs the Batlle 1988 urine anion gap and must not invent an RTA or diarrhea diagnosis from the sign of the gap.

## When not to use

- Not a diagnosis. Negative versus positive is a Batlle 1988 interpretive band for NH4+ excretion, not a diagnosis of RTA or GI bicarbonate loss.
- Does not measure urine ammonium. mEq/L equals mmol/L for these monovalent ions.
- Does not interpret urine pH or net acid excretion beyond the Na + K − Cl gap.

## Formula

```
urine_anion_gap_mmol_l = urine_sodium_mmol_l + urine_potassium_mmol_l - urine_chloride_mmol_l
```

## Citation

[The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis](https://doi.org/10.1056/NEJM198803033180902)
Batlle DC, Hizon M, Cohen E, Gutterman C, Gupta R
N Engl J Med. 1988;318(10):594-599
DOI: [10.1056/NEJM198803033180902](https://doi.org/10.1056/NEJM198803033180902)

## Worked example

### Na 20, K 30, Cl 90 (negative UAG)

Given: `urine_chloride_mmol_l=90, urine_potassium_mmol_l=30, urine_sodium_mmol_l=20`

1. UAG = 20 + 30 − 90 = −40.0 mmol/L
2. band negative (increased NH4+ / GI bicarbonate loss in Batlle 1988; not a diagnosis)


### Na 80, K 40, Cl 70 (positive UAG)

Given: `urine_chloride_mmol_l=70, urine_potassium_mmol_l=40, urine_sodium_mmol_l=80`

1. UAG = 80 + 40 − 70 = 50.0 mmol/L
2. band positive (impaired NH4+ / RTA in Batlle 1988; not a diagnosis)


## Also searched as

- urine anion gap
- urinary anion gap
- UAG
- urine net charge
- Batlle urinary anion gap
- urinary NH4 surrogate

## Parameters

- `urine_sodium_mmol_l` (number, required): Urine sodium in mmol/L (same as mEq/L). Range 1-300.
- `urine_potassium_mmol_l` (number, required): Urine potassium in mmol/L (same as mEq/L). Range 1-200.
- `urine_chloride_mmol_l` (number, required): Urine chloride in mmol/L (same as mEq/L). Range 1-300.

## 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/urine_anion_gap`
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": [
    {
      "urine_chloride_mmol_l": "90",
      "urine_potassium_mmol_l": "30",
      "urine_sodium_mmol_l": "20"
    },
    {
      "urine_chloride_mmol_l": "90",
      "urine_potassium_mmol_l": "30",
      "urine_sodium_mmol_l": "20"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/urine-anion-gap

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/urine_anion_gap",
  "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": "Batlle DC, Hizon M, Cohen E, Gutterman C, Gupta R",
        "doi": "10.1056/NEJM198803033180902",
        "id": "batlle-1988",
        "source": "N Engl J Med. 1988;318(10):594-599",
        "title": "The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis"
      },
      "formula": "urine_anion_gap",
      "formula_expression": "urine_anion_gap_mmol_l = urine_sodium_mmol_l + urine_potassium_mmol_l - urine_chloride_mmol_l",
      "urine_sodium_mmol_l": 20.0,
      "uag_band": "negative",
      "urine_anion_gap_mmol_l": -40.0,
      "urine_chloride_mmol_l": 90.0,
      "urine_potassium_mmol_l": 30.0
    },
    {
      "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": "Batlle DC, Hizon M, Cohen E, Gutterman C, Gupta R",
        "doi": "10.1056/NEJM198803033180902",
        "id": "batlle-1988",
        "source": "N Engl J Med. 1988;318(10):594-599",
        "title": "The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis"
      },
      "formula": "urine_anion_gap",
      "formula_expression": "urine_anion_gap_mmol_l = urine_sodium_mmol_l + urine_potassium_mmol_l - urine_chloride_mmol_l",
      "urine_sodium_mmol_l": 20.0,
      "uag_band": "negative",
      "urine_anion_gap_mmol_l": -40.0,
      "urine_chloride_mmol_l": 90.0,
      "urine_potassium_mmol_l": 30.0
    }
  ]
}
```

## Response fields

- `formula` (string): urine_anion_gap
- `formula_expression` (string): Exact expression used
- `urine_sodium_mmol_l` (number): Urine sodium used, mmol/L
- `urine_potassium_mmol_l` (number): Urine potassium used, mmol/L
- `urine_chloride_mmol_l` (number): Urine chloride used, mmol/L
- `urine_anion_gap_mmol_l` (number): Urine anion gap in mmol/L (mEq/L), 1 decimal
- `uag_band` (string): negative (UAG < 0; Batlle: increased NH4+, GI bicarbonate loss), near_zero (UAG = 0), or positive (UAG > 0; Batlle: impaired NH4+, RTA). A band, not a diagnosis.
- `citation` (object): Batlle et al. NEJM 1988 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": "Batlle DC, Hizon M, Cohen E, Gutterman C, Gupta R",
    "doi": "10.1056/NEJM198803033180902",
    "id": "batlle-1988",
    "source": "N Engl J Med. 1988;318(10):594-599",
    "title": "The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis"
  },
  "formula": "urine_anion_gap",
  "formula_expression": "urine_anion_gap_mmol_l = urine_sodium_mmol_l + urine_potassium_mmol_l - urine_chloride_mmol_l",
  "urine_sodium_mmol_l": 20.0,
  "uag_band": "negative",
  "urine_anion_gap_mmol_l": -40.0,
  "urine_chloride_mmol_l": 90.0,
  "urine_potassium_mmol_l": 30.0
}
```

## Errors

- HTTP 400 `invalid_urine_sodium`: urine_sodium_mmol_l must be a number from 1 to 300. Returned before settlement; you are not charged.
- HTTP 400 `invalid_urine_potassium`: urine_potassium_mmol_l must be a number from 1 to 200. Returned before settlement; you are not charged.
- HTTP 400 `invalid_urine_chloride`: urine_chloride_mmol_l must be a number from 1 to 300. 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

- [Anion gap](https://magentlab.com/docs/anion-gap) — Compute the serum anion gap from sodium, chloride, and bicarbonate, with or without potassium, using the Emmett–Narins 1977 formulas. formula is required.
- [Stool osmotic gap](https://magentlab.com/docs/stool-osmotic-gap) — Compute the Eherer–Fordtran fecal osmotic gap from stool sodium and potassium, using measured stool osmolality when supplied or 290 mOsm/kg when omitted.

## 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 echoing accepted, payload, and extensions when present).
- 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.
- 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.