Urea Reduction Ratio (URR)
URR measures the percentage of urea removed during dialysis. KDOQI targets ≥65% minimum, ≥70% optimal.
Why This Health Metric Matters
Why: URR is the simplest dialysis adequacy metric—only pre and post BUN needed. KDOQI recommends monthly monitoring.
How: URR = ((Pre-BUN - Post-BUN) / Pre-BUN) × 100. Use slow-flow sampling for post-dialysis BUN.
- ●KDOQI minimum 65%
- ●70% target optimal
- ●Time has greatest impact on URR
Sample Clinical Scenarios — Click to Load
Dialysis Parameters
⚠️For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
URR 65% approximates Kt/V 1.2-1.3
— Nephrology
Adding 30 min can increase URR by 5-8%
— Clinical practice
Key Takeaways
- • KDOQI minimum URR target is 65%; many nephrologists target 70%+
- • URR correlates with Kt/V but does not account for ultrafiltration
- • Post-dialysis BUN rebound can make URR appear better than true clearance
- • Treatment time has the greatest impact on URR—add time before increasing flow
- • Use slow-flow sampling for accurate post-dialysis BUN
💡 Did You Know?
URR Definition
Percentage of urea removed from blood during dialysis
— KDOQI
65% Minimum
KDOQI recommends URR ≥65% for adequate dialysis
— KDOQI 2015
URR vs Kt/V
URR 65% approximates Kt/V 1.2-1.3
— Nephrology
Time Matters
Adding 30 min can increase URR by 5-8%
— Clinical practice
BUN Rebound
Urea redistributes 10-20% after dialysis
— Physiology
Slow-Flow
Reduce pump to 50-100 mL/min before post sample
— Sampling protocol
📖 How It Works
URR is calculated by comparing pre- and post-dialysis BUN. The formula (Pre-Post)/Pre × 100 gives the percentage of urea removed. Use slow-flow sampling for post-dialysis BUN to minimize rebound effects.
🎯 Expert Tips
⚖️ URR Adequacy Thresholds
| URR | Kt/V (approx) | Adequacy |
|---|---|---|
| <60% | <1.0 | Inadequate |
| 60-64% | 1.0-1.2 | Borderline |
| 65-69% | 1.2-1.4 | Adequate |
| ≥70% | >1.4 | Optimal |
❓ FAQ
Check access recirculation, treatment time, blood flow, catheter function, or dialyzer clotting.
Very high URR (>80%) is rarely harmful but may indicate very long treatment times.
URR is simpler—only two BUN values. Kt/V needs weight and UF data.
Increase treatment time (most effective), blood flow, dialyzer efficiency, or frequency.
📊 Key Numbers
📚 Official Sources
⚠️ Disclaimer
Medical Disclaimer: This calculator is for educational purposes only. URR interpretation requires clinical context. Always consult a qualified nephrologist for dialysis prescription decisions.