-
USP 61 Micro Test
Can anyone think of a reason why two identical samples, taken from the same lot of material at the same time, but sent to two different micro labs, would see two wildly different results? One lab passed the material, the other said it failed miserably.
@MarkBroussard, @Eli, @The_Microbiologist? Anyone else?
-
8 Replies
-
@BobZ:
Have each of these labs produced reliable results for you in the past, or is one of them a new lab to your organization?Perhaps your sample got mislabeled at one of the labs is the only thing I can think of since they would both be following the same testing protocol.Do you know what the contaminating organism was in the test that failed? -
I suppose cleanliness of the testing lab could have an impact. Maybe they use different organisms?
It’s a good question. -
Could one sample have been contaminated during transport?
-
Well, that’s the thing…
We require our supplier to test their product for micro (and pass) before they ship it to us. Then, once it gets here, we send a sample to our micro lab. Well, the last two or three shipments from them have failed the USP 61 micro test on our side, but the material passed before they shipped it to us.In an effort to rule out contamination during shipping, etc., I had the supplier pull 2 samples at the same time from his latest lot, and send 1 sample to the outside lab he usually uses, and one to the outside lab that we use. His passed, ours failed.So, now I need to know why - these aren’t challenge, or PET tests, they are just plate counts. -
Well, it seems there is a problem with one of the two labs.
I would suggest you have your supplier pull two samples prior to shipment and send one to his usual lab and the second sample to a completely different lab that neither of your organizations use, but a mutually-agreed upon lab.You, Bob, might do the same on your end. Upon receipt, pull two samples and send one to your usual lab and a second to a completely different lab.That way, you might be able to nail down which lab has a QA problem … yours or your suppliers.’ -
Could it be a shipping problem, something temperature dependent?
-
If it’s a shipping problem, then it’s a preservative problem. Bob said that he had the supplier send a sample from the supplier’s location to Bob’s lab … that sample also failed the test at Bob’s lab.
If the material cannot withstand shipping extremes, then it is likely that the preservative is inactivated during transport.@Bob:I am assuming from your comments that you have been purchasing this same product from this supplier for some time now. Something obviously has changed in the past couple of months … prior to, I am assuming that the supplier’s product had a history of passing at your lab?So, the question is: What has changed, if anything on the supplier’s side … change in manufacturing, preservative, etc. If nothing has changed supplier-side, then the problem has to be with one of the two labs. -
did you ever figure this out?
- different growth media
- different methods
- one of the labs is contaminated and doesn’t realize it yet - (false positive)
- one of the labs is cooking the books (false negative)
- speed of arrival; one lab is closer than another
send the sample that your lab says is contaminated, to the lab that says their sample, isn’t.
if it comes back clean, then one of the two labs has a serious problem.
prior to sending out the sample, you should request exact details from each of the labs, as to their testing methods, and growth media. this is so they can’t backtrack.
Log in to reply.
