Fractional excretion of urea calculator
Compares how much urea reaches the urine with creatinine filtration: plasma urea 40, urine urea 200, plasma creatinine 1.2 and urine creatinine 80 give a FEUrea of 7.5%, below the 35% teaching cutoff. Built for classroom checks and study. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Plasma urea
- 40
- Urine urea
- 200
- Plasma creatinine
- 1.2
- Urine creatinine
- 80
- Feurea
- 7.5
- Feurea rounded
- 7.5
- Feurea unit
- percent
- Band
- low
Fractional excretion of urea, often written FEUrea, is a classic nephrology teaching ratio that compares how much urea ends up in the urine relative to creatinine filtration. Clinicians and students use it when interpreting acute kidney injury patterns, especially when loop diuretics make the fractional excretion of sodium harder to interpret. This capability accepts four laboratory concentrations—plasma (or serum) urea, urine urea, plasma creatinine, and urine creatinine—applies the standard percentage formula, and returns a stable FEUrea value plus a transparent educational band at the commonly discussed thirty-five percent cutoff. Units cancel when plasma and urine share the same unit for each analyte, so you may send conventional milligrams per decilitre panels or another consistent pair without a conversion step inside the engine. Missing fields, non-numeric strings, zeros, negatives, and out-of-range readings fail with a clear invalid input error and are never charged.
What FEUrea measures and which four lab values you need
Fractional excretion of urea expresses urea clearance as a percentage of creatinine clearance using simultaneous plasma and urine samples. The standard teaching formula multiplies urine urea by plasma creatinine, divides by the product of plasma urea and urine creatinine, then multiplies by one hundred to report a percent. Because both numerator and denominator carry concentration units, those units cancel when plasma urea and urine urea share one unit and plasma creatinine and urine creatinine share one unit—commonly milligrams per decilitre on US basic metabolic and urine chemistry panels.
Practical bounds keep classroom and consumer inputs sane while still covering critical-care extremes: plasma urea from zero point zero one through five hundred, urine urea through five thousand, plasma creatinine through thirty, and urine creatinine through one thousand in the same concentration scale you chose. Do not mix SI urea in millimoles per litre against milligrams-per-decilitre urine without converting first—consistency across the pair is the contract, not a hidden unit converter.
Classroom uses and practical limits
Call the free in-browser fractional excretion of urea calculator for classroom demos, nursing and medical-school homework checks, and quick personal learning without reimplementing the ratio in every spreadsheet. Prefer consistent conventional or SI units within each analyte; if your UI only collects whole numbers, send integers and the engine still accepts numeric strings. Authors shipping SDKs can map band into colour chips for educational thresholds you define yourself and show the formula string on a teaching card.
Keep expectations educational: this is a calculation and learning tool, not a diagnostic medical device, and people with symptoms, known kidney disease, volume depletion, or medication changes should follow professional medical advice rather than any single automated FEUrea value alone.
What you can do with it
AKI teaching apps and worksheets
Apps demonstrate FEUrea when discussing diuretic-confounded FENa cases without re-coding the four-term ratio on every client.
FAQ
What do the low and high bands mean?
Educational labels only: low is FEUrea under 35%, high is 35% or above. They match a common teaching cutoff used when discussing prerenal versus intrinsic patterns and are not a lab-specific reference interval or diagnosis.
What happens if a field is missing or zero?
Zero or non-positive values would break the ratio; missing or non-numeric fields are also rejected and not charged.
Is the fractional excretion of urea calculator free?
The browser tool runs free on your device.
Do I need the same units for all four values?
Plasma and urine urea must share one unit, and plasma and urine creatinine must share one unit. Units cancel inside the ratio; do not mix inconsistent scales without converting first.
When is FEUrea used instead of the sodium version?
Mainly when loop diuretics make the fractional excretion of sodium harder to interpret. Clinicians and students then turn to FEUrea when reading acute kidney injury patterns, always within the wider clinical picture.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/feurea \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"plasma_urea":40,"urine_urea":200,"plasma_creatinine":1.2,"urine_creatinine":80}'const res = await fetch("https://api.kit.forhosting.com/health/feurea", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"plasma_urea": 40,
"urine_urea": 200,
"plasma_creatinine": 1.2,
"urine_creatinine": 80
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/feurea",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"plasma_urea": 40,
"urine_urea": 200,
"plasma_creatinine": 1.2,
"urine_creatinine": 80
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/feurea", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"plasma_urea":40,"urine_urea":200,"plasma_creatinine":1.2,"urine_creatinine":80}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"plasma_urea":40,"urine_urea":200,"plasma_creatinine":1.2,"urine_creatinine":80}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/feurea", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"plasma_urea": 40,
"urine_urea": 200,
"plasma_creatinine": 1.2,
"urine_creatinine": 80
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.feurea",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
The browser tool runs free on your device; the prepaid API charges $0.002 per successful item when servers and SDKs need the same deterministic contract.
What FEUrea measures and which four lab values you need
Send required fields plasma_urea, urine_urea, plasma_creatinine, and urine_creatinine as finite positive numbers; documented aliases such as serum_urea, p_urea, purea, blood_urea, u_urea, uurea, serum_creatinine, p_creatinine, pcr, u_creatinine, and ucr are accepted when your client prefers shorter keys. Every value must be strictly greater than zero because the formula multiplies and divides these four scalars; zero or negative concentrations fail with invalid_input rather than inventing a result. Identical inputs always yield identical JSON because the path is pure arithmetic with no network, no language model, no random seed, and no wall clock.
Reading FEUrea, educational band, response fields, and errors
On success the response echoes the four input concentrations with stable rounding, reports feurea as the full-precision percent used for banding, and feurea_rounded to two decimal places for UI display. The field feurea_unit is always the string percent. The band field is low when FEUrea is strictly less than thirty-five and high when FEUrea is greater than or equal to thirty-five; band_threshold restates that cutoff so clients never hard-code a magic number. Many textbooks discuss low FEUrea as more consistent with a prerenal pattern and higher FEUrea as more consistent with intrinsic renal injury when the clinical context already supports acute kidney injury evaluation—especially when diuretics confound fractional sodium excretion—but those discussions are educational framing only and never a standalone diagnosis. formula restates the equation as a single string, and method is always feurea_percent so downstream code can branch without sniffing response shapes. Use feurea when you need stable numeric comparison in automated tests; use feurea_rounded when you show the number next to a lab card or teaching slide. Missing required fields, empty strings, non-finite values, any non-positive concentration, and out-of-range readings all fail with invalid_input and are not charged. Do not confuse this endpoint with BUN-to-creatinine serum ratios, eGFR creatinine equations, fractional excretion of sodium, or full nephrology decision engines—those serve different search intents and different input contracts. This product only combines four concentrations into FEUrea percent and applies a transparent teaching band.
API usage, pricing, product workflows, and practical limits
Send a JSON body with the four required concentration fields using the same unit for each plasma–urine pair. Use the prepaid API when a health education SaaS, electronic worksheet, simulation lab, tutoring platform, or school LMS needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair this endpoint with your own laboratory unit policy—confirm whether your panel reports urea or blood urea nitrogen and convert BUN to urea if your local formula expects urea—then store feurea, feurea_rounded, and band alongside the raw inputs for dashboards and export columns.
Integration use cases
Nursing and medical-school homework
Students submit simultaneous plasma and urine urea and creatinine values and pin expected FEUrea percent and band JSON in automated checkers.
Simulation labs and SaaS backends
Server pipelines that already store chem and urine fields call a prepaid endpoint for FEUrea instead of duplicating formulas in every language.
Technical questions
How is fractional excretion of urea calculated?
FEUrea (%) = (urine_urea × plasma_creatinine) / (plasma_urea × urine_creatinine) × 100. Send those four required fields; the response includes feurea, feurea_rounded, band, and a readable formula string.