# Chen kinetic eGFR (KeGFR)

KeGFR

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/kegfr`
HTML: https://magentlab.com/docs/kegfr
Markdown: https://magentlab.com/docs/kegfr.md

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

## What it computes

Compute Chen 2013 kinetic eGFR (KeGFR) from two plasma creatinines, the hours between them, a caller-assigned steady-state creatinine and corresponding eGFR/CrCl, and MaxΔPCr/Day. magent does not compute MDRD or CKD-EPI.

## When to use

When plasma creatinine is changing acutely and an agent needs published Chen 2013 KeGFR rather than a CKD-EPI snapshot or a language-model guess. Endpoints should be <48-72 h apart (Chen). Not a dialysis prescription.

## When not to use

- Not a medical device. Not a CKD-EPI result and not a dialysis prescription.
- magent does not compute MDRD or CKD-EPI. The caller assigns steady_state_egfr (5-200) as the corresponding eGFR/CrCl for steady_state_creatinine_mg_dl.
- Creatinine is mg/dL only. max_delta_pcr_mg_dl_day is required (Chen usual default 1.5); magent does not omit it. KeGFR is clamped at 0 when the (1 − ratio) term would be negative.

## Formula

```
kegfr_ml_min = (steady_state_creatinine_mg_dl * steady_state_egfr / mean_pcr_mg_dl) * (1 - (24 * delta_pcr_mg_dl) / (delta_hours * max_delta_pcr_mg_dl_day)); mean_pcr_mg_dl = (creatinine_1_mg_dl + creatinine_2_mg_dl) / 2; delta_pcr_mg_dl = creatinine_2_mg_dl - creatinine_1_mg_dl; clamp kegfr_ml_min at 0 when (1 - ratio) is negative (Chen 2013)
```

## Citation

[Retooling the Creatinine Clearance Equation to Estimate Kinetic GFR when the Plasma Creatinine Is Changing Acutely](https://doi.org/10.1681/ASN.2012070653)
Chen S
J Am Soc Nephrol. 2013;24(6):877-888
DOI: [10.1681/ASN.2012070653](https://doi.org/10.1681/ASN.2012070653)

## Worked example

### Steady-state Cr 1.0, eGFR 90, 24 h, MaxΔPCr/Day 1.5

Given: `creatinine_1_mg_dl=1, creatinine_2_mg_dl=1, delta_hours=24, max_delta_pcr_mg_dl_day=1.5, steady_state_creatinine_mg_dl=1, steady_state_egfr=90`

1. MeanPCr = (1 + 1) / 2 = 1.0; ΔPCr = 1 - 1 = 0
2. term = 1 - (24 × 0) / (24 × 1.5) = 1
3. KeGFR = (1 × 90 / 1.0) × 1 = 90.0 (formula reduces to CrCl)


## Also searched as

- kinetic GFR
- kinetic estimated GFR
- Chen KeGFR
- kinetic creatinine clearance
- non-steady-state GFR
- changing plasma creatinine GFR
- KeGFR Chen 2013

## Parameters

- `creatinine_1_mg_dl` (number, required): First plasma creatinine in mg/dL (0.1-20). mg/dL only.
- `creatinine_2_mg_dl` (number, required): Second plasma creatinine in mg/dL (0.1-20). mg/dL only.
- `delta_hours` (number, required): Hours between creatinine_1 and creatinine_2 (1-72). Chen: endpoints <48-72 h apart.
- `steady_state_creatinine_mg_dl` (number, required): Steady-state plasma creatinine in mg/dL (0.1-20) corresponding to steady_state_egfr. mg/dL only.
- `steady_state_egfr` (number, required): Caller-assigned eGFR/CrCl in mL/min corresponding to steady_state_creatinine_mg_dl (5-200). magent does not compute MDRD or CKD-EPI.
- `max_delta_pcr_mg_dl_day` (number, required): Maximum creatinine rise per day in mg/dL (0.5-3). Chen usual default 1.5. Required; magent does not omit it.

## 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/kegfr`
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": [
    {
      "creatinine_1_mg_dl": "1",
      "creatinine_2_mg_dl": "1",
      "delta_hours": "24",
      "max_delta_pcr_mg_dl_day": "1.5",
      "steady_state_creatinine_mg_dl": "1",
      "steady_state_egfr": "90"
    },
    {
      "creatinine_1_mg_dl": "1",
      "creatinine_2_mg_dl": "1",
      "delta_hours": "24",
      "max_delta_pcr_mg_dl_day": "1.5",
      "steady_state_creatinine_mg_dl": "1",
      "steady_state_egfr": "90"
    }
  ]
}
```

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

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/kegfr",
  "items": [
    {
      "units": "mL/min",
      "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": "Chen S",
        "doi": "10.1681/ASN.2012070653",
        "id": "chen-2013",
        "pmid": "23704286",
        "source": "J Am Soc Nephrol. 2013;24(6):877-888",
        "title": "Retooling the Creatinine Clearance Equation to Estimate Kinetic GFR when the Plasma Creatinine Is Changing Acutely"
      },
      "formula": "kegfr",
      "formula_expression": "kegfr_ml_min = (steady_state_creatinine_mg_dl * steady_state_egfr / mean_pcr_mg_dl) * (1 - (24 * delta_pcr_mg_dl) / (delta_hours * max_delta_pcr_mg_dl_day)); mean_pcr_mg_dl = (creatinine_1_mg_dl + creatinine_2_mg_dl) / 2; delta_pcr_mg_dl = creatinine_2_mg_dl - creatinine_1_mg_dl; clamp kegfr_ml_min at 0 when (1 - ratio) is negative (Chen 2013)",
      "creatinine_1_mg_dl": 1.0,
      "creatinine_2_mg_dl": 1.0,
      "delta_hours": 24.0,
      "delta_pcr_mg_dl": 0.0,
      "kegfr_ml_min": 90.0,
      "max_delta_pcr_mg_dl_day": 1.5,
      "mean_pcr_mg_dl": 1.0,
      "steady_state_creatinine_mg_dl": 1.0,
      "steady_state_egfr": 90.0
    },
    {
      "units": "mL/min",
      "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": "Chen S",
        "doi": "10.1681/ASN.2012070653",
        "id": "chen-2013",
        "pmid": "23704286",
        "source": "J Am Soc Nephrol. 2013;24(6):877-888",
        "title": "Retooling the Creatinine Clearance Equation to Estimate Kinetic GFR when the Plasma Creatinine Is Changing Acutely"
      },
      "formula": "kegfr",
      "formula_expression": "kegfr_ml_min = (steady_state_creatinine_mg_dl * steady_state_egfr / mean_pcr_mg_dl) * (1 - (24 * delta_pcr_mg_dl) / (delta_hours * max_delta_pcr_mg_dl_day)); mean_pcr_mg_dl = (creatinine_1_mg_dl + creatinine_2_mg_dl) / 2; delta_pcr_mg_dl = creatinine_2_mg_dl - creatinine_1_mg_dl; clamp kegfr_ml_min at 0 when (1 - ratio) is negative (Chen 2013)",
      "creatinine_1_mg_dl": 1.0,
      "creatinine_2_mg_dl": 1.0,
      "delta_hours": 24.0,
      "delta_pcr_mg_dl": 0.0,
      "kegfr_ml_min": 90.0,
      "max_delta_pcr_mg_dl_day": 1.5,
      "mean_pcr_mg_dl": 1.0,
      "steady_state_creatinine_mg_dl": 1.0,
      "steady_state_egfr": 90.0
    }
  ]
}
```

## Response fields

- `formula` (string): kegfr
- `formula_expression` (string): Exact Chen 2013 KeGFR expression, including mean, signed delta, and clamp
- `creatinine_1_mg_dl` (number): First plasma creatinine in mg/dL
- `creatinine_2_mg_dl` (number): Second plasma creatinine in mg/dL
- `delta_hours` (number): Hours between the two creatinines
- `steady_state_creatinine_mg_dl` (number): Steady-state plasma creatinine in mg/dL
- `steady_state_egfr` (number): Caller-assigned corresponding eGFR/CrCl in mL/min
- `max_delta_pcr_mg_dl_day` (number): Maximum creatinine rise per day in mg/dL
- `mean_pcr_mg_dl` (number): Arithmetic mean of creatinine_1_mg_dl and creatinine_2_mg_dl
- `delta_pcr_mg_dl` (number): Signed creatinine_2_mg_dl minus creatinine_1_mg_dl
- `kegfr_ml_min` (number): Kinetic eGFR in mL/min, 1 decimal. Clamped at 0. Not a CKD-EPI result.
- `units` (string): mL/min
- `citation` (object): Chen J Am Soc Nephrol 2013 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "units": "mL/min",
  "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": "Chen S",
    "doi": "10.1681/ASN.2012070653",
    "id": "chen-2013",
    "pmid": "23704286",
    "source": "J Am Soc Nephrol. 2013;24(6):877-888",
    "title": "Retooling the Creatinine Clearance Equation to Estimate Kinetic GFR when the Plasma Creatinine Is Changing Acutely"
  },
  "formula": "kegfr",
  "formula_expression": "kegfr_ml_min = (steady_state_creatinine_mg_dl * steady_state_egfr / mean_pcr_mg_dl) * (1 - (24 * delta_pcr_mg_dl) / (delta_hours * max_delta_pcr_mg_dl_day)); mean_pcr_mg_dl = (creatinine_1_mg_dl + creatinine_2_mg_dl) / 2; delta_pcr_mg_dl = creatinine_2_mg_dl - creatinine_1_mg_dl; clamp kegfr_ml_min at 0 when (1 - ratio) is negative (Chen 2013)",
  "creatinine_1_mg_dl": 1.0,
  "creatinine_2_mg_dl": 1.0,
  "delta_hours": 24.0,
  "delta_pcr_mg_dl": 0.0,
  "kegfr_ml_min": 90.0,
  "max_delta_pcr_mg_dl_day": 1.5,
  "mean_pcr_mg_dl": 1.0,
  "steady_state_creatinine_mg_dl": 1.0,
  "steady_state_egfr": 90.0
}
```

## Errors

- HTTP 400 `invalid_kegfr`: creatinine_1_mg_dl and creatinine_2_mg_dl must be 0.1-20, delta_hours 1-72, and max_delta_pcr_mg_dl_day 0.5-3 (Chen 2013 KeGFR). Returned before settlement; you are not charged.
- HTTP 400 `invalid_egfr`: egfr_ml_min_1_73m2 must be a number from 5 to 200 (caller-assigned eGFR; magent does not compute MDRD or CKD-EPI). 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

- [CKD-EPI 2021 eGFR](https://magentlab.com/docs/egfr) — Compute race-free CKD-EPI 2021 creatinine eGFR in mL/min/1.73m2.
- [Cockcroft–Gault CrCl](https://magentlab.com/docs/crcl) — Compute Cockcroft–Gault creatinine clearance in mL/min using total body weight.

## 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.