# Urea Reduction Ratio (URR) — Dialysis Adequacy 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. > Canonical page: https://elysiatools.com/en/tools/urea-reduction-ratio - **Category:** Health - **Keywords:** urea reduction ratio, URR, dialysis adequacy, hemodialysis, BUN, KDOQI, nephrology, renal, urea, dialysis dose ## 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. ## Inputs - **Pre-dialysis BUN (mg/dL)** (number): Pre-dialysis blood urea nitrogen in mg/dL. Must be positive. - **Post-dialysis BUN (mg/dL)** (number): Post-dialysis blood urea nitrogen in mg/dL. Must be ≥0 and less than pre-BUN. - **Decimal Places** (number) ## 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 - Enter the pre-dialysis BUN in mg/dL. - Enter the post-dialysis BUN in mg/dL; it must be at least 0 and lower than the pre-dialysis value. - The calculator subtracts post-BUN from pre-BUN, divides by pre-BUN, and multiplies by 100. - The 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. ## Frequently asked questions ### 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. ## Related tools - [A-a Gradient (Alveolar-Arterial O₂)](https://elysiatools.com/en/tools/a-a-gradient-calculator): Calculate the alveolar-arterial O₂ gradient to distinguish hypoxemia causes. PAO₂ = FiO₂×(P_atm−47) − PaCO₂/0.8; A-a = PAO₂ − PaO₂. Normal ≈ (Age+10)/4. Elevated → V/Q mismatch, shunt, diffusion impairment. Derived from StatPearls, LITFL, Cornell PICU, and Martin 1999. 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