Which staining method is best for demonstrating glycogen in tissue?

• A. Periodic acid-Schiff (PAS)
• B. Hematoxylin and eosin
• C. Masson's trichrome
• D. Luxol fast blue

Answer: (A)

Glycogen is a carbohydrate stored inside cells, so you need a stain that specifically highlights polysaccharides. The Periodic acid-Schiff method does just that: periodic acid oxidizes the sugar residues to aldehydes, and the Schiff reagent then couples with those aldehydes to produce a bright magenta color in the cytoplasm where glycogen is stored. This makes glycogen conspicuous against the surrounding tissue. The other stains shown do not target carbohydrates: Hematoxylin and eosin is a general stain for overall morphology, Masson's trichrome highlights connective tissue like collagen, and Luxol fast blue stains myelin. If you want to confirm that the magenta staining is due to glycogen specifically, you can use a diastase digestion control before PAS; glycogen will be digested and the stain will disappear, confirming the presence of glycogen.