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Control Slides
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Control Slides

Question.

May I ask, in all your opinions, Who is supplying the best control slides for clinical settings? Both Special Stain and IHC? What would you like to see in your control slides? What don't you want to see- long lead times, quality? As for Research, what are your requirements?

Answer.

Here's the opinion of an 85 year old pathologist who in the course of his training spent a year doing histochemical research. In my experience, pathologists aren't allowed much input in the selection of controls.

Anyone doing special stains needs to be able to evaluate the control slides for adequacy.

Control tissue needs to be fixed and processed in the same way as the tissue being investigated.

Some stains (like trichromes) need controls only to keep the inspectors happy, while others need a control run and looked at every time. Stains for micro-organisms require controls, for example. These controls should be tissue sections with active infection, not bugs embedded in gelatin. These controls are hard to get.

Acid-fast stains require a control for the particular organism being looked for. Usually Mycobacterium tuberculosis. The best controls I've ever seen were lungs from rhesus monkeys with active tuberculosis, which a lot of them imported for research purposes had. The veterinary pathologists used to do these necropsies. Obviously one monkey can keep you supplied for a lifetime.

Myco. leprae is a notoriously fickle stainer, and controls are hard to get, since very few animals can be infected with human leprosy. One leprous armadillo liver can supply a laboratory for many years.

I think atypical mycobacteria usually get tuberculosis controls.

The chromic acid methenamine silver stain is best controlled with the particular fungus you're looking for. The most demanding control is histoplasma in old inactive lung lesions. Candida is probably too easy.

PAS really isn't a satisfactory fungus stain.

Tissue Gram stains are vastly over-rated, and should be done away with. I think most people use a diseased appendix.

If you're still doing a Giemsa or toluidine blue stain for Helicobacter, it should be controlled with a known positive for that organism.

Amyloid controls have to be repeatedly tested to make sure they work. Human amyloidosis is a rare disease, and autopsy material these days is much rarer. I wonder if amyloid from animal controls has ever come into use. (Amyloidosis is supposed to be rather easily produced in mice.) I've never been able to get an answer to this question. Supposedly amyloid in sections still in wax on the slide (as controls are commonly prepared) isn't stable for more than a month.

I don't have enough technical experience with immunohistochemistry to have any ideas.

Bob Richmond, Maryville TN

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