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Urea Reduction Ratio (URR) — Dialysis Adequacy

· Last updated：2026-08-05

This tool is for informational purposes only and does not constitute medical, financial, or legal advice; consult a qualified professional for advice.

Calculate the Urea Reduction Ratio (URR) for a single hemodialysis session: URR (%) = (Pre-BUN − Post-BUN) / Pre-BUN × 100. KDOQI recommends a minimum URR ≥65% and a target dose ≥70%. URR is a simple adequacy marker but is being phased out in favor of Kt/V, which also accounts for urea generation and volume contraction. Derived from the KDOQI Clinical Practice Guideline for Hemodialysis Adequacy. Valid for single hemodialysis sessions with BUN drawn pre- and immediately post-treatment; not for peritoneal dialysis. Not medical advice.

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Tool usage guide

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Key facts

Category
Health
Input types
number
Output type
json
Sample coverage
4
API ready
Yes

Overview

Calculate the Urea Reduction Ratio (URR) for one hemodialysis session using pre-dialysis and post-dialysis BUN values. The calculator applies URR = (Pre-BUN − Post-BUN) / Pre-BUN × 100% and compares the result with KDOQI reference thresholds of 65% minimum and 70% target. This tool is not medical advice.

When to use

  • Estimate URR for a single hemodialysis session with BUN measured before and immediately after treatment.
  • Check whether a calculated URR reaches the KDOQI minimum of 65% or target of 70%.
  • Review a simple dialysis adequacy marker before confirming adequacy with Kt/V and clinical judgment.

How it works

  1. 1Enter the pre-dialysis BUN in mg/dL.
  2. 2Enter the post-dialysis BUN in mg/dL; it must be at least 0 and lower than the pre-dialysis value.
  3. 3The calculator subtracts post-BUN from pre-BUN, divides by pre-BUN, and multiplies by 100.
  4. 4The JSON result includes the URR percentage, unit, status, calculation method, and a note about the KDOQI thresholds.

Use cases

  • Dialysis staff can calculate and document the URR from pre- and post-treatment BUN measurements.
  • Nephrology learners can verify the URR formula and compare sample results with KDOQI thresholds.
  • Clinical reviewers can quickly identify results below the 65% minimum for further assessment.

Examples

1. URR reaches the target threshold

Dialysis clinician

Background

A single hemodialysis session has a pre-dialysis BUN of 90 mg/dL and a post-dialysis BUN of 27 mg/dL.

Problem

Calculate the percentage reduction and determine whether it meets the KDOQI target.

How to use

Enter 90 for Pre-dialysis BUN, 27 for Post-dialysis BUN, and use 4 decimal places.

{"preBun":90,"postBun":27,"decimalPlaces":4}

Outcome

The calculator returns URR = 70.0000%, with the status Target met (≥70%).

2. URR falls below the minimum threshold

Nephrology student

Background

A hemodialysis session has a pre-dialysis BUN of 80 mg/dL and a post-dialysis BUN of 30 mg/dL.

Problem

Check whether the calculated URR meets the minimum KDOQI reference value.

How to use

Enter 80 for Pre-dialysis BUN, 30 for Post-dialysis BUN, and use 4 decimal places.

FAQ

What is the URR formula?

URR (%) = (Pre-BUN − Post-BUN) / Pre-BUN × 100.

What URR value is considered adequate?

The referenced KDOQI thresholds are a minimum of 65% and a target of 70% or higher.

What inputs does this calculator require?

It requires pre-dialysis BUN and post-dialysis BUN values in mg/dL. Decimal places are optional.

Can I use URR for peritoneal dialysis?

No. This calculator is intended for a single hemodialysis session.

Is URR a replacement for Kt/V?

No. URR is a simple marker and does not account for urea generation or volume contraction; Kt/V should be used to confirm full adequacy.

Hub

Renal Function, Dialysis, and Dose-Model Checks

Compare kidney-function formulas, dialysis adequacy metrics, and renal medication math in an educational workflow that avoids patient-specific dosing or diagnosis.

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{"preBun":80,"postBun":30,"decimalPlaces":4}

Outcome

The calculator returns URR = 62.5000%, with the status Below minimum (<65%).