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ADEQUACY:

To compute Urea Reduction Ratio (URR), you need accurate pre- and post-dialysis blood samples. The technique matters a lot—especially the post sample—because errors can falsely increase or decrease URR.

🩸 PRE-DIALYSIS (Pre-BUN)
👉 Goal: get the true baseline BUN
When:
Before starting dialysis (before heparin, before blood pump starts)
How:
Draw from arterial (red) port of the dialysis access
If using catheter: draw from arterial lumen
If AVF/AVG: use needle before connecting lines
Key Tip:
✔ Do NOT start dialysis yet
✔ Avoid dilution (no saline, no priming contamination)
🩸 POST-DIALYSIS (Post-BUN)
👉 This is where most errors happen!
There are 2 accepted methods, but one is preferred:
✅ 1. Slow Flow Method (Recommended – per KDOQI)
Steps:
At end of dialysis → reduce blood flow to 100 mL/min
Wait 15–30 seconds
Draw sample from arterial port
Then stop dialysis
Why?
Prevents “access recirculation” and falsely low BUN
⚠️ 2. Stop Flow Method (Less preferred)
Steps:
Stop blood pump completely
Clamp lines
Draw from arterial port immediately
Risk:
Can give inaccurate results if timing is off
📊 URR Formula
Here’s how URR is computed:
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🎯 Target URR (per KDOQI)
✅ ≥ 65% = adequate dialysis
⚠️ Common Mistakes to Avoid
❌ Drawing post sample too fast (high blood flow)
❌ Not waiting before sampling
❌ Drawing from venous line
❌ Dilution from saline or rinse-back
❌ Wrong timing (after rinse-back = inaccurate!)

🎯 Adequacy Target
✅ URR ≥ 65% (minimum for adequate hemodialysis)
Preferred with:
3x/week dialysis
≥ 3–4 hours/session

💡 FocusSym Tip
👉 “Slow it down before you draw.”
= prevents falsely high URR

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