Kidney · LIVE

Transtubular potassium gradient (TTKG)

TTKG

Compute the transtubular potassium gradient (TTKG) from plasma potassium, urine potassium, plasma osmolality, and urine osmolality using Ethier et al. 1990.

LIVE $0.005 USDC GET /api/calc/ttkg

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

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

What it computes

Compute the transtubular potassium gradient (TTKG) from plasma potassium, urine potassium, plasma osmolality, and urine osmolality using Ethier et al. 1990.

When to use

When an agent needs the published Ethier 1990 TTKG from paired potassium and osmolality and must not invent a potassium-disorder diagnosis from the number.

When not to use

• Not a medical device.
• Not a potassium-disorder diagnosis. Numeric TTKG only; magent does not assign diagnostic bands.
• TTKG is not valid when urine is hypotonic relative to plasma (urine osmolality ≤ plasma osmolality; water diuresis). Those inputs return HTTP 400.

Formula

ttkg = (urine_k_mmol_l / potassium_mmol_l) / (urine_osm_mosm_kg / plasma_osm_mosm_kg)

Citation

Title

The transtubular potassium concentration in patients with hypokalemia and hyperkalemia

Authors

Ethier JH, Kamel KS, Magner PO, Lemann J Jr, Halperin ML

Source

Am J Kidney Dis. 1990;15(4):309-315

DOI

10.1016/S0272-6386(12)80076-X

Worked example

Also searched as

• transtubular potassium gradient
• TTKG
• transtubular potassium concentration
• Ethier TTKG
• urine potassium gradient
• transtubular K gradient

Try

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

/api/calc/ttkg?potassium_mmol_l=4.0&urine_k_mmol_l=40&plasma_osm_mosm_kg=300&urine_osm_mosm_kg=600

Full URL: https://api.magentlab.com/api/calc/ttkg?potassium_mmol_l=4.0&urine_k_mmol_l=40&plasma_osm_mosm_kg=300&urine_osm_mosm_kg=600

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/ttkg?potassium_mmol_l=4.0&urine_k_mmol_l=40&plasma_osm_mosm_kg=300&urine_osm_mosm_kg=600"

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/ttkg 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": [
    {
      "plasma_osm_mosm_kg": "300",
      "potassium_mmol_l": "4.0",
      "urine_k_mmol_l": "40",
      "urine_osm_mosm_kg": "600"
    },
    {
      "plasma_osm_mosm_kg": "300",
      "potassium_mmol_l": "4.0",
      "urine_k_mmol_l": "40",
      "urine_osm_mosm_kg": "600"
    }
  ]
}

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/ttkg",
  "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": "Ethier JH, Kamel KS, Magner PO, Lemann J Jr, Halperin ML",
        "doi": "10.1016/S0272-6386(12)80076-X",
        "id": "ethier-1990",
        "pmid": "2321642",
        "source": "Am J Kidney Dis. 1990;15(4):309-315",
        "title": "The transtubular potassium concentration in patients with hypokalemia and hyperkalemia"
      },
      "formula": "ethier",
      "formula_expression": "ttkg = (urine_k_mmol_l / potassium_mmol_l) / (urine_osm_mosm_kg / plasma_osm_mosm_kg)",
      "potassium_mmol_l": 4.0,
      "plasma_osm_mosm_kg": 300.0,
      "ttkg": 5.0,
      "urine_k_mmol_l": 40.0,
      "urine_osm_mosm_kg": 600.0
    },
    {
      "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": "Ethier JH, Kamel KS, Magner PO, Lemann J Jr, Halperin ML",
        "doi": "10.1016/S0272-6386(12)80076-X",
        "id": "ethier-1990",
        "pmid": "2321642",
        "source": "Am J Kidney Dis. 1990;15(4):309-315",
        "title": "The transtubular potassium concentration in patients with hypokalemia and hyperkalemia"
      },
      "formula": "ethier",
      "formula_expression": "ttkg = (urine_k_mmol_l / potassium_mmol_l) / (urine_osm_mosm_kg / plasma_osm_mosm_kg)",
      "potassium_mmol_l": 4.0,
      "plasma_osm_mosm_kg": 300.0,
      "ttkg": 5.0,
      "urine_k_mmol_l": 40.0,
      "urine_osm_mosm_kg": 600.0
    }
  ]
}

Response

Example JSON

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

{
  "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": "Ethier JH, Kamel KS, Magner PO, Lemann J Jr, Halperin ML",
    "doi": "10.1016/S0272-6386(12)80076-X",
    "id": "ethier-1990",
    "pmid": "2321642",
    "source": "Am J Kidney Dis. 1990;15(4):309-315",
    "title": "The transtubular potassium concentration in patients with hypokalemia and hyperkalemia"
  },
  "formula": "ethier",
  "formula_expression": "ttkg = (urine_k_mmol_l / potassium_mmol_l) / (urine_osm_mosm_kg / plasma_osm_mosm_kg)",
  "potassium_mmol_l": 4.0,
  "plasma_osm_mosm_kg": 300.0,
  "ttkg": 5.0,
  "urine_k_mmol_l": 40.0,
  "urine_osm_mosm_kg": 600.0
}

Client errors (HTTP 400)

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

Related tools

• FEUrea — Compute fractional excretion of urea (FEUN) from BUN, urine urea nitrogen, plasma creatinine, and urine creatinine.
• 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.

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.
• 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.