A special stain is a type of test that helps pathologists see details in a tissue sample that cannot be seen with the more common hematoxylin and eosin stain. Pathologists perform this type of test by adding a coloured dye (the stain) to a tissue sample which is then examined under a microscope. The stain causes the tissue to change colour. The colour depends on the type of stain used and the tissue.
Types of special stains
There are hundreds of different special stains available and the type selected will depend on the question your pathologist is trying to answer. For example, some infectious micro-organisms such as fungi or bacteria are almost invisible when examined with hematoxylin and eosin. When a special stain is added to the tissue, these micro-organisms turn black or red which makes them much easier to see.
Here are some of the most commonly used special stains:
- PAS/D – PAS/D is commonly used to highlight fungal organisms and biological materials such as mucin and glycogen.
- Masson trichrome – The Masson stain is commonly used to highlight a type of scar tissue in tissue that pathologists call fibrosis.
- Mucicarmine – Mucicarmine is used to a type of biological material called mucin easier to see inside cells. Pathologists often use this stain to make the diagnosis of adenocarcinoma.
- Ziehl-Neelsen – This stain is used to highlight the micro-organisms that cause tuberculosis in tissue, however, it can also be used to identify other types of micro-organisms.
- Elastic – This stain allows pathologists to see a specialized type of protein called elastic fibers inside a tissue sample. Elastic fibers are found normally around blood vessels and on the outer surface of the lung (the pleura). The stain is usually used by pathologists to see if the elastic fibers have been damaged either by cancer cells or an inflammatory process.