Each histochemical and immunohistochemical stain should be accompanied by positive and negative controls which can help to ensure that the staining procedure worked properly.
Inventories must be kept for:
(1) control slides
(2) blocks from which control slides are prepared
Issues:
(1) frequency of use
(2) number of stains being performed
(3) availability and cost of block procurement
(4) distribution of target material in tissue block
Requirements:
(1) The control is processed the same as study material.
(2) The control is informative around the level of analytical sensitivity.
A block of human tissue showing the target is ideal but may not be available. Alternatives may include:
(1) tissue from another species (selected to avoid anti-animal antibodies in reagents)
(2) target material and cellular elements suspended in agar or gelatin
To reduce the need for separate inventory it is possible to combine cores from several controls into a single block which allows for one slide to be used for different stains. The problem here is that each core must be representative.
One strategy is to restrict the stain menu to those that can be performed economically, with uncommon stains sent to a reference laboratory. Some reference laboratories require that the stain be interpreted by a staff pathologist, which can impact cost and billing.
