Fractional excretion of urea calculator
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.
Run — free
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. 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.
How to use it
Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.
Check your inputs
Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.
Use it again or automate it
Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.
What you can do with it
Get an answer now
Enter one set of values and see the result without building a spreadsheet or script.
Compare scenarios
Change one value at a time and rerun the calculation to understand what affects the result.
Automate repeated work
Use the API when the same calculation needs to run inside your product or workflow.
FAQ
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.
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?
The request fails with invalid_input. 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. API calls use prepaid KIT balance at $0.002 per successful item; validation failures are not charged.
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.
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. |