I find that there are several areas where cross-contamination can be
occuring and you really have to follow the system through.
For example, do you check the slide with the block as part of your IQA? If
they do not match it shows that the contamination could have come from the
grossing area as well as the ususal culprit, the water bath. You then have
to check both areas; is the pathologist as clean as she/he could be?;is the
board being washed down between samples?;are the forceps rinsed between
samples?; is the histologist working in a clean area when performing
microtomy?;are your water baths filled with fresh water every working day?
and so on.
What you have to do is realistically go to every stage where cross
contamination could occur and examine what steps are taken to ensure
cleanliness. For example, the xylene bath which you mount your sections
from, how often is it changed? Vey often it is the last thing that is
thought of as it rarely gets contaminated with alcohol (unless you have a
bunch of students like mine plus very high humidity!) and gets forgotten.
Very often bits of sections float off and sit in this pot just waiting for
another slide to come along! It could be that your sections are lifting from
the slides and bits are sitting in the stains, in which case, you won't ever
see them until it is too late (another reason for checking the slide with
the block). Then you can solve the problem of why your sections are lifting
and this may then solve your problem.
How many people do you have cutting? Is your contamination squames? It may
be that a particular individual who has dry skin and is a bit slack at
dipping their fingers in the water bath when retrieving sections. And so on.
You just have to take a step back and look at the whole scenario and without
knowing your system, I can't be more specific.
Sultan Qaboos University,
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