OOS of Bacterial Endotoxin Tests

We use kinetic turbidimetric method for BET of parenteral products. OOS occurs every now and then on CV% values, endotoxin standards and PPC% but lately it got worse. The only reasonable explanation I can come up with is pipetting error caused by analyst. Training of analyst repeated, pipette’s calibration and performance checked, disposal materials checked, it all seems fine. I failed to find root cause and out of ideas.

I would deeply appreciate if you’ll leave any lead to follow.

Thank you.


Endo testing is sensitive and could have outliners. Based on what you have described, the CV% was the measurements of variations between your sample repetitions. By saying that I would look into several items that could have the CV% higher than the acceptable limit are:

  1. the accessories that are used in for testing
    a. the pipettes (you did)
    b. Analyst pipet techniques
    c. Microplates
    d. Reagents should obtain room temperature 5-10 minutes before use
    e. Sample prep steps (ensure that you sample is consistently homogeneous throughout testing)
    f. Perform re-evaluation on your BioTek equipment
    g. Re-validate you inhibition/enhancement testing
    h. You may purchase and use different type of glassware for your dilutions
    i. Add your lysate into sample wells more quickly and consistently

It looks like you have issue with testing techniques than the samples.

Hope this helps.

Good luck,

1 has any trend been established? What product shows these deviant results or is it all products? All technicians or just one?
2 In addition to the post above, have you checked endotoxin load of your pipette tips?
3 Any new batches of disposables/LAL water/Reagents/standards used that may be related to these deviant results?

Hi Claudia,

I like your well thoughts. Good strategies.