Regarding whether to stain for the proper intensity on the control only,
or also monitor the patient samples, there are times when stopping the
staining because the control was perfect is inappropriate. For instance,
some labs do not have a pneumocystis control, and when staining for this
microbe, most samples need slightly longer time in the silver than if
you were demonstrating aspergillus (commonly used as a fungus control
for GMS). Additionally, patients with large balls of fungus in their
tissues show normal to weak staining of the fungus as compared to the
control, and the center of the fungal colony is almost always very
weakly or not stained. In this case, it is helpful to leave the slides
in a little longer to try to additionally demonstrate as much of the
material as you can (without going too far, of course!).

Section thickness can also play a role in staining intensity for some
special stains. When possible, always screen the patient slides for
positivity. It also gives you a heads up more potential positive control
material is available.

Teri Johnson, HT(ASCP)QIHC
Managing Director Histology Facility
Stowers Institute for Medical Research
1000 E. 50th St.
Kansas City, MO 64110

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