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Magent FEUN Calculator (Fractional Excretion of Urea)
x402
Magent FEUN Calculator (Fractional Excretion of Urea) is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-15).
Calculates fractional excretion of urea nitrogen (FEUN) from BUN, urine urea nitrogen, and plasma/urine creatinine using the Carvounis 2002 formula, for use when diuretics make FENa unreliable.
Price / call$0.005
Success—
StatusUnknown
How this service works
Fractional excretion of urea (FEUN) from BUN, urine urea nitrogen, and plasma/urine creatinine (Carvounis 2002). Use when diuretics make FENa unhelpful. Deterministic published formula with citation; not a diagnosis.
Output
Returns the computed fractional excretion of urea nitrogen (FEUN) as a percentage, along with an interpretation (e.g. prerenal if FEUN <35%, intrinsic/ATN if ≥35%) based on the Carvounis 2002 published thresholds. The response is a deterministic arithmetic result, not a diagnosis.
Example use cases
AKI workup on diuretic therapy
“My ICU patient is on furosemide so FENa is unreliable — can you calculate FEUN to help differentiate prerenal from intrinsic AKI? BUN is 55 mg/dL, urine urea is 420 mg/dL, serum creatinine is 2.8 mg/dL, urine creatinine is 110 mg/dL.”
ED acute kidney injury triage
“Patient came in with elevated creatinine and oliguria, but they take a loop diuretic daily — compute the fractional excretion of urea for me: BUN 38 mg/dL, urine urea nitrogen 310 mg/dL, plasma creatinine 1.9 mg/dL, urine creatinine 85 mg/dL.”
Nephrology consult note automation
“I'm writing a nephrology consult note and need the FEUN value. Labs: BUN 60 mg/dL, urine urea 500 mg/dL, serum creatinine reported in SI units as 212 µmol/L, urine creatinine 8850 µmol/L.”
Technical details
Endpoint
GEThttps://api.magentlab.com/api/calc/feureaWhen to prefer
Use this endpoint when a patient is on diuretics (loop, thiazide) making FENa unreliable as a prerenal AKI marker. FEUN is the preferred alternative per Carvounis 2002 and is the standard recommendation in nephrology guidelines for diuretic-treated patients. Prefer the sibling FENa endpoint when the patient is not on diuretics. This endpoint is the right choice when you have BUN and urine urea values alongside creatinine measurements.
Side effects
- Missing required parameters (bun_mg_dl or urine_urea_mg_dl) returns a validation error
- Out-of-range values (e.g. BUN outside 1–200 mg/dL, urine urea outside 1–2000 mg/dL, urine creatinine outside 1–500 mg/dL) may return an error or flagged result
- If neither creatinine_mg_dl nor creatinine_umol_l is provided, the computation cannot proceed
- If neither urine_creatinine_mg_dl nor urine_creatinine_umol_l is provided, computation fails
- Payment failure via x402 protocol results in 402 response before computation is attempted
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"path": "/api/calc/feurea",
"count": 2,
"items": [
{
"units": "%",
"formula": "carvounis",
"citation": {
"id": "carvounis-2002",
"doi": "10.1046/j.1523-1755.2002.00683.x",
"title": "Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure",
"source": "Kidney Int. 2002;62(6):2223-2229",
"authors": "Carvounis CP, Nisar S, Guro-Razuman S"
},
"bun_mg_dl": 20,
"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.",
"carvounis_band": "low",
"feurea_percent": 20,
"creatinine_mg_dl": 2,
"urine_urea_mg_dl": 200,
"formula_expression": "FEUrea_percent = 100 * (urine_urea_mg_dl * plasma_creatinine_mg_dl) / (bun_mg_dl * urine_creatinine_mg_dl)",
"urine_creatinine_mg_dl": 100
},
{
"units": "%",
"formula": "carvounis",
"citation": {
"id": "carvounis-2002",
"doi": "10.1046/j.1523-1755.2002.00683.x",
"title": "Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure",
"source": "Kidney Int. 2002;62(6):2223-2229",
"authors": "Carvounis CP, Nisar S, Guro-Razuman S"
},
"bun_mg_dl": 20,
"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.",
"carvounis_band": "low",
"feurea_percent": 20,
"creatinine_mg_dl": 2,
"urine_urea_mg_dl": 200,
"formula_expression": "FEUrea_percent = 100 * (urine_urea_mg_dl * plasma_creatinine_mg_dl) / (bun_mg_dl * urine_creatinine_mg_dl)",
"urine_creatinine_mg_dl": 100
}
]
}
}Tags
x402
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