Periodic acid-Schiff stain

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Periodic acid-Schiff (PAS) is a staining method used in histology and pathology. This method is primarily used to identify glycogen in tissues. The reaction of periodic acid selectively oxidizes the glucose residues, creates aldehydes that react with the Schiff reagent and creates a purple-magenta color. A suitable basic stain is often used as a counterstain.

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

PAS staining can be used to distinguish between different types of glycogen storage disease. However, it has uses beyond this, such as being indicative of certain forms of cancer, such as Paget's disease, or in staining macrophages in Whipple's disease.