What this calculator does
Urea reduction ratio (URR) works out percentage drop in blood urea over one haemodialysis session, a dialysis-adequacy check. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaURR = (pre-dialysis BUN − post-dialysis BUN) / pre-dialysis BUN × 100
The inputs explained
| Field | What to enter |
|---|---|
| Pre-dialysis BUN (mg/dL) | A number, measured in mg/dL. Starts at 60. |
| Post-dialysis BUN (mg/dL) | A number, measured in mg/dL. Starts at 18. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with pre-dialysis bun
Every other input is held at the calculator’s starting values while pre-dialysis bun varies. Select any row to load that scenario into the calculator.
How the answer changes with pre-dialysis bun
| Pre-dialysis BUN (mg/dL) | Urea reduction ratio | Adequacy threshold | Reading |
|---|---|---|---|
| 30 | 40.0% | 65% or higher is generally considered adequate | Below the usual adequacy threshold: worth discussing with the treating team |
| 45 | 60.0% | 65% or higher is generally considered adequate | Below the usual adequacy threshold: worth discussing with the treating team |
| 60 | 70.0% | 65% or higher is generally considered adequate | At or above the usual adequacy threshold |
| 90 | 80.0% | 65% or higher is generally considered adequate | At or above the usual adequacy threshold |
| 120 | 85.0% | 65% or higher is generally considered adequate | At or above the usual adequacy threshold |
| 180 | 90.0% | 65% or higher is generally considered adequate | At or above the usual adequacy threshold |