Accepted Bacterial Growth + Endotoxin Limits
Per AAMI/ISO 23500 & ISO 11663:2014 — water, dialysate, and drain
📊 These are the standards most units follow worldwide.
“Before dialyzer” = dialysate at the machine inlet · “Drain” = spent dialysate leaving the machine.
1. Water used to prepare dialysate
Sampled at RO loop, post-treatment, or machine inlet water
| Standard |
Bacteria |
Endotoxin |
Action Level |
| AAMI/ISO “Standard” water |
<100 CFU/mL |
<0.25 EU/mL |
≥50 CFU/mL or ≥0.125 EU/mL → disinfect |
| AAMI/ISO “Ultrapure” water |
<0.1 CFU/mL |
<0.03 EU/mL |
Any growth or >0.015 EU/mL → investigate |
2. Dialysate at the point before dialyzer
This is “conventional dialysate” sampled from the Hansen connectors or sample port before it enters the dialyzer
| Standard |
Bacteria |
Endotoxin |
Action Level |
| AAMI/ISO “Standard” dialysate |
<100 CFU/mL |
<0.5 EU/mL |
≥50 CFU/mL or ≥0.25 EU/mL → disinfect machine + water |
| AAMI/ISO “Ultrapure” dialysate |
<0.1 CFU/mL |
<0.03 EU/mL |
Any growth or >0.015 EU/mL → investigate |
Key point: Most guidelines now push for ultrapure dialysate <0.1 CFU/mL + <0.03 EU/mL at the dialyzer inlet because chronic endotoxin exposure drives inflammation, CV disease, and poor ESA response.
3. Spent dialysate at the drain
Sampled from machine drain line after it leaves the dialyzer
There is NO official AAMI/ISO limit for the drain because:
- It's waste fluid — it never touches the patient again
- It will always have bacteria from the patient's blood compartment + biofilm in the dialyzer/drain line
- Counts can be 10³ to 10⁶ CFU/mL normally
But why units still test the drain:
- Trending: If drain counts suddenly jump 2–3 logs, it suggests dialyzer membrane leak, severe biofilm in machine, or high bacteria in fresh dialysate
- Infection control: Some countries set internal action limits like <200 CFU/mL in spent dialysate to flag machine contamination
- Research: High drain counts correlate with backfiltration risk if TMP goes positive
Practical rule used by many units:
If fresh dialysate is <100 CFU/mL but drain is >10⁴ CFU/mL, investigate the machine/dialyzer. If fresh dialysate itself is >100 CFU/mL, the drain doesn't matter — you already failed.
Important testing notes
🧫 Method matters
- Use Tryptic Soy Agar or R2A, 17–23°C, 7 days
- Blood agar at 37°C misses water bacteria
📊 Volume & frequency
- Plate 1–10 mL for water, 0.1–1 mL for dialysate
- Report as CFU/mL
- AAMI: minimum monthly for water + dialysate
- After repairs or disinfection failures → repeat immediately
⚠️ Action levels = 50% of max
If limit is 100 CFU/mL, you must act at 50 CFU/mL.
Bottom line for your unit
Before dialyzer: Goal should be ultrapure <0.1 CFU/mL + <0.03 EU/mL. Acceptable minimum is <100 CFU/mL + <0.5 EU/mL, but act at 50 CFU/mL.
Drain: No official limit. Use it for trending. If drain explodes but inlet is clean, check machine. If inlet fails, drain is irrelevant.
Reality check: 9–35% of water and 11–19% of dialysate samples still exceed these limits worldwide, which is why “ultrapure” is hard.