Urea Reduction Ratio
Provide pre- and post-haemodialysis blood urea nitrogen (BUN) to calculate URR. Compare with guideline targets for dialysis adequacy.
Post-BUN should be obtained using the slow-flow or stop-pump technique.
How to Use This Calculator
Collect pre/post BUN values
Draw pre-dialysis BUN immediately before treatment and post-BUN at treatment completion using approved sampling techniques.
Enter concentrations in mg/dL
URR is unitless; mg/dL is standard for BUN reporting. Ensure post-BUN is lower than pre-BUN for a valid reduction.
Interpret against guideline targets
URR ≥65% (preferably ≥70%) is recommended for thrice-weekly haemodialysis according to KDOQI guidelines.
Formula
URR (%) = ((Pre-BUN − Post-BUN) ÷ Pre-BUN) × 100
Approximate Kt/V ≈ −ln(1 − URR)
(For precise Kt/V, use the Daugirdas II equation with ultrafiltration volume and session length.)
Full Description
Urea reduction ratio is a quick indicator of dialysis efficacy, representing the fractional decrease in BUN during a haemodialysis session. While Kt/V provides a more comprehensive kinetics-based assessment, URR remains widely used for rapid quality checks. Persistent low URR should trigger evaluation of treatment duration, dialyser clearance, vascular access function, and patient adherence to prescribed schedule.
Frequently Asked Questions
How often should URR be measured?
Many dialysis units measure URR monthly. KDOQI recommends at least monthly adequacy assessments in stable patients.
What if post-BUN was drawn incorrectly?
Incorrect sampling (e.g., from venous line without slow flow) can produce false high or low URR. Repeat using standard slow-flow technique.
Does URR apply to peritoneal dialysis?
No. Peritoneal dialysis adequacy uses Kt/V. URR is designed for in-centre haemodialysis sessions.
How does session length affect URR?
Shorter treatments reduce URR by limiting urea removal. Increasing dialysis time is a straightforward way to improve URR and Kt/V.