# CKiD U25 eGFR Calculator (Pierce 2021)

> CKiD U25 eGFR Calculator (Pierce 2021) is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-14).

Calculates estimated GFR for patients aged 1–25 using the Pierce 2021 CKiD U25 formula with creatinine, cystatin C, or both markers

## Facts

- Endpoint: GET https://api.magentlab.com/api/calc/ckid_u25
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/ckid-u25-egfr-calculator-pierce-2021-2d9c9c2a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_gfrb0_154rn6UivrJCAv1

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability ckid-u25-egfr-calculator-pierce-2021-2d9c9c2a
```

Example prompt: Calculate the CKiD U25 eGFR for a 12-year-old male who is 145 cm tall with a serum creatinine of 0.7 mg/dL and a cystatin C of 0.9 mg/L using the Pierce 2021 formula.

## When to prefer this

Use this endpoint when you need the Pierce 2021 CKiD U25 eGFR specifically for patients aged 1–25, as opposed to the adult Schwartz bedside 0.413 formula or adult CKD-EPI equations. It is particularly appropriate when the patient age falls outside the adult range or when you have cystatin C available for a more accurate combined estimate. Do not use for CKD staging, drug dosing decisions, or patients over 25.

## Known failure modes

- Age outside the 1–25 year range returns a validation error
- Missing required paired inputs (e.g., creatinine without height) returns an error
- Creatinine or cystatin C values outside plausible ranges (e.g., creatinine > 20 mg/dL) may be rejected
- Invalid sex enum value returns a schema error
- Providing neither creatinine nor cystatin C returns an error — at least one marker is required

## How this service works

CKiD U25 eGFR (Pierce 2021) for ages 1-25: age- and sex-dependent K times height in meters over creatinine (mg/dL), or K over cystatin C (mg/L), or the average of both when both markers are given. Height may be cm or inches; creatinine may be mg/dL or µmol/L. Not the Schwartz 2009 bedside 0.413 formula, not a drug dose, and not a CKD stage. Not a medical device.

## Output

Returns a numeric eGFR estimate (mL/min/1.73m²) computed via the Pierce 2021 CKiD U25 age- and sex-dependent K formula. When both creatinine and cystatin C are provided, returns the average of both eGFR paths. Indicates which calculation path was used (creatinine-based, cystatin C-based, or combined).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "required": [
      "age_years",
      "sex"
     ],
     "properties": {
      "sex": {
       "enum": [
        "female",
        "male"
       ],
       "type": "string",
       "description": "Sex used by Pierce 2021 Table 2 K. female or male."
      },
      "age_years": {
       "type": "number",
       "description": "Age in years (1-25, fractional ages allowed). Pierce 2021 CKiD U25 age-dependent K is evaluated at that age. Not the adult 18-120 clamp."
      },
      "height_cm": {
       "type": "number",
       "description": "Height in centimeters (50-250). Required with creatinine for the creatinine or combined path. Converted to meters in the equation. Provide height_cm or height_in. Not required for cystatin-only."
      },
      "height_in": {
       "type": "number",
       "description": "Height in inches (20-98). Converted as cm = in * 2.54."
      },
      "cystatin_c_mg_l": {
       "type": "number",
       "description": "Serum cystatin C in mg/L (0.2-10). Required for the cystatin-only or combined path. Height is not required when this is the only marker."
      },
      "creatinine_mg_dl": {
       "type": "number",
       "description": "Serum creatinine in mg/dL (0.1-20). Required with height for the creatinine or combined path. Provide this or creatinine_umol_l."
      },
      "creatinine_umol_l": {
       "type": "number",
       "description": "Serum creatinine in µmol/L (9-1768). Converted as mg/dL = µmol/L / 88.42."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/ckid-u25-egfr-calculator-pierce-2021-2d9c9c2a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.magentlab.com](https://www.zero.xyz/host/api.magentlab.com/llms.txt)