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Processing artifact – delayed start
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Processing artifact – delayed start


We have terrible processing artifact if tissue sits in the formalin-filled retort (at ambient temperature) for too long (more than 10-12 hours) before a delayed process starts. The longer the wait, the worse it looks.

We have Tissue Tek VIP 5 processors, and we process luminal gastrointestinal biopsies exclusively. This artifact typically affects a few specimens per day (~2% or less), even though everything is done on the same processor; it may affect all tissue portions in a cassette or only some of the tissue in that cassette. Some tissue portions may only have the artifact on one half with the other half looking perfectly fine. The techs sometimes note the tissue feeling "crunchy" at the time of embedding and / or at the time of microtomy. These tissues tend to suffer greater chatter artifact and have trouble sticking to the slides. The sections look just as bad on recuts as the originals. Re-processing does not seem to help at all. 

If the cassettes sit in formalin in a container outside of the processor for days before the processor is loaded (with subsequent immediate start), things look perfectly fine. When we have staff around to start the processor immediately upon loading cassettes and empty immediately upon completion, the tissue looks perfectly fine.

Answer 1.

I would check the level of the formalin after it has been pumped into the retort.

Tony Henwood MSc, BAppSc, GradDipSysAnalys, CT(ASC), FFSc(RCPA) (Retired), University of Western Sydney

Answer 2.

We have had 2 reasons why we saw processing issues like this:

1. I recently found out on our VIP 5 they did not turn the level sensors on during install. These sensors are known to error so often, Sakura tells technicians to set the default to off. All the processor can sense is pressure and time. So it may be that the formalin is not filling all the way. You are noticing this on delayed runs, but on those runs are you often stacking trays? If so, isolate the cases in the upper trays and review.

2. We found a clogged line. This happens with the formalin lines if you don’t do the hot water flush often enough. This can be an even bigger issue if you recycle and re-buffer your formalin (we do not). Good luck!

Chuck Bacon, HTL(ASCP)CM, Supervisor Histology, Baystate Medical Center

Answer 3.

I am wondering if you are getting air bubbles/pockets in the cassettes themselves. Are you using mesh cassettes? Are you loading the trays with cassettes into an empty retort and then starting the delayed program? If so, air pockets could be forming in the cassette and around the tissue pieces. Since there is no p/v cycle running yet, those air pockets may be just sitting there and the exposed tissue pieces may be getting dried out.

I suggest that once the retort is full and in ambient mode, open retort and move the cassette trays around a bit and see if air bubbles are rising from the cassettes. When the trays of cassettes sit on the bench in formalin waiting to go on the VIP, there may be enough movement when moving the container, etc, that any air pockets are disrupted and the tissues are not exposed to air pockets.

Amysue Ruppert, Marshfield Labs Histology

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