Target URR for Patients Undergoing Hemodialysis

The target Urea Reduction Ratio (URR) for patients undergoing hemodialysis should be 70%, with a minimally adequate dose of 65%. 1

Recommended Dialysis Adequacy Targets

For patients receiving hemodialysis three times per week with residual kidney function (Kr) less than 2 mL/min/1.73 m², the minimally adequate dose should be a URR of 65% (corresponding to a single-pool Kt/V of 1.2) 1
The target dose should be a URR of 70% (corresponding to a single-pool Kt/V of 1.4) 1, 2
These targets are based on evidence from the HEMO Study, which showed that higher doses beyond these targets did not significantly improve mortality or hospitalization outcomes 1

The relationship between URR and Kt/V is affected by ultrafiltration volume, with URR decreasing as ultrafiltration increases 1
Timing of post-dialysis blood sampling significantly impacts URR values:
- Sampling immediately after dialysis may falsely elevate URR due to access recirculation 1
- Sampling 30-60 minutes after dialysis completion provides the most accurate measurement but is impractical in clinical settings 1
- The recommended approach is the slow-flow/stop-pump technique, which provides reproducible results 1, 3

For patients with residual kidney function (Kr) ≥ 2 mL/min/1.73 m², the minimum session spKt/V can be reduced, but the target should still be at least 15% greater than the minimum dose 1
Missed or shortened treatments significantly impact outcomes and should be monitored and minimized 1, 2
No evidence supports different URR targets based on demographic characteristics:
- Diabetic patients do not require higher minimum doses of hemodialysis 1
- No evidence supports lower URR targets for patients of different racial backgrounds 1

Using URR alone without considering residual kidney function may lead to incorrect assessment of dialysis adequacy 4
Post-dialysis urea rebound can significantly affect URR calculations, with rebound averaging 22.4% in some studies 5
The stop-dialysate-flow method has not been validated in pediatric dialysis patients 1
With large dialyzers used at relatively lower blood flow rates, dialyzer outlet blood may still have substantially lower urea concentration than inlet blood after the standard waiting period 1

URR should be measured within the first month after initiating dialysis therapy and at least once every 4 months thereafter 2
To improve URR in patients not meeting targets, consider:
- Increasing blood flow rate 3
- Increasing dialyzer surface area 3
- Extending dialysis session duration if necessary 3
A simplified approach using URR ≥ 67% provides a reasonable means of assessing adequacy of intermittent hemodialysis, especially in acute kidney injury where volume of distribution of urea is highly variable 6