[Histonet] Control Slides (Ken M)

[Bob Richmond]

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.

Bob Richmond
Maryville TN

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