Which staining technique is used to visualize glycogen and carbohydrate-rich substances in liver tissue?

• A. Periodic acid–Schiff (PAS)
• B. Hematoxylin and eosin (H&E)
• C. Gram stain
• D. Ziehl-Neelsen stain

Answer: (A)

Period periodic acid–Schiff staining highlights carbohydrates by converting vicinal diols in sugars into aldehyde groups that react with Schiff reagent to give a magenta color. In the liver, glycogen stored in hepatocytes and other carbohydrate-rich substances such as mucopolysaccharides and basement membranes stain vividly with PAS, making it a primary tool for visualizing glycogen content and other carbohydrate-rich structures. A useful enhancement is diastase digestion (PAS-D): when glycogen is present, removing it with diastase eliminates the magenta staining, helping confirm glycogen specifically. By contrast, routine H&E is a general stain for tissue architecture and does not selectively highlight glycogen, while Gram stain and Ziehl-Neelsen target microorganisms, not carbohydrate storage.