Periodic acid–Schiff stain

Periodic acid–Schiff (PAS) is a staining method used to detect polysaccharides (such as glycogen) and mucosubstances (such as glycoproteins, glycolipids and mucins) in tissues.

PAS staining is mainly used for staining structures containing a high proportion of carbohydrate macromolecules (glycogen, glycoprotein, proteoglycans), typically found in e.g. connective tissues, mucus, the glycocalyx, and basal laminae.

The diastase negative slide will show a magenta staining where glycogen is present within a section of tissue.

If the PAS stain will be performed on tissue, the recommended fixative is 10% neutral-buffered formalin or Bouin solution.

Glutaraldehyde is not recommended because free aldehyde groups may be available to react with the Schiff reagent, which may result in false positive staining.