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FENa Calculator (Fractional Excretion of Sodium)
x402
FENa Calculator (Fractional Excretion of Sodium) 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).
Computes fractional excretion of sodium (FENa%) from plasma sodium, urine sodium, plasma creatinine, and urine creatinine using the Espinel 1976 formula for oliguric acute renal failure stratification.
Price / call$0.005
Success—
StatusUnknown
How this service works
Fractional excretion of sodium (FENa) from plasma and urine sodium and creatinine. Espinel 1976 oliguric ARF strata. Deterministic published formula with citation; not a diagnosis.
Output
Returns the computed FENa percentage along with the Espinel 1976 oliguric ARF stratum (e.g., prerenal vs. intrinsic renal failure classification), based on the deterministic published formula. Not a clinical diagnosis.
Example use cases
Prerenal vs intrinsic AKI triage
“My ICU patient has new oliguria — serum sodium 141 mmol/L, urine sodium 12 mmol/L, serum creatinine 3.1 mg/dL, urine creatinine 85 mg/dL. Calculate the FENa and tell me if it's consistent with prerenal AKI by Espinel criteria.”
Nephrology consult documentation
“I need the FENa value for my consult note: plasma Na 136 mmol/L, urine Na 45 mmol/L, plasma creatinine 310 µmol/L, urine creatinine 6200 µmol/L. Please compute it with the 1976 formula.”
Automated renal panel interpretation
“Run the FENa calculation on these labs — serum sodium 139 mmol/L, spot urine sodium 8 mmol/L, serum creatinine 1.8 mg/dL, urine creatinine 200 mg/dL — and flag whether this suggests low or high fractional excretion.”
Technical details
Endpoint
GEThttps://api.magentlab.com/api/calc/fenaWhen to prefer
Use this endpoint when you need a deterministic, citation-backed FENa calculation (Espinel 1976) for oliguric ARF stratification and want automatic unit conversion between mg/dL and µmol/L for creatinine inputs. Prefer over manual calculation or LLM-estimated values when reproducibility and published-formula fidelity matter.
Side effects
- Missing required parameter sodium_mmol_l or urine_sodium_mmol_l returns 400 error
- No creatinine value provided (neither mg/dL nor µmol/L for plasma or urine) returns validation error
- Values outside physiologic ranges (e.g. sodium < 110 or > 160 mmol/L) may be rejected
- Both creatinine unit variants provided simultaneously may cause ambiguity
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"path": "/api/calc/fena",
"count": 2,
"items": [
{
"formula": "fena",
"citation": {
"id": "espinel-1976",
"doi": "10.1001/jama.1976.03270060029022",
"title": "The FENa test. Use in the differential diagnosis of acute renal failure",
"source": "JAMA. 1976;236(6):579-581",
"authors": "Espinel CH"
},
"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.",
"fena_percent": 0.29,
"sodium_mmol_l": 140,
"espinel_stratum": "prerenal",
"creatinine_mg_dl": 2,
"formula_expression": "FENa_percent = 100 * (urine_sodium_mmol_l * plasma_creatinine_mg_dl) / (plasma_sodium_mmol_l * urine_creatinine_mg_dl)",
"urine_sodium_mmol_l": 20,
"urine_creatinine_mg_dl": 100
},
{
"formula": "fena",
"citation": {
"id": "espinel-1976",
"doi": "10.1001/jama.1976.03270060029022",
"title": "The FENa test. Use in the differential diagnosis of acute renal failure",
"source": "JAMA. 1976;236(6):579-581",
"authors": "Espinel CH"
},
"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.",
"fena_percent": 0.29,
"sodium_mmol_l": 140,
"espinel_stratum": "prerenal",
"creatinine_mg_dl": 2,
"formula_expression": "FENa_percent = 100 * (urine_sodium_mmol_l * plasma_creatinine_mg_dl) / (plasma_sodium_mmol_l * urine_creatinine_mg_dl)",
"urine_sodium_mmol_l": 20,
"urine_creatinine_mg_dl": 100
}
]
}
}Tags
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