Which method is more specific for glycogen demonstration than the best carmine technique?

• A. PAS with or without diastase
• B. Best carmine
• C. H&E
• D. Silver stain

Answer: (A)

Periodic acid–Schiff stains carbohydrates by converting sugars to aldehydes that react with Schiff reagent, giving a magenta color. Glycogen tends to give a strong PAS signal, but many other polysaccharides can also stain. The trick to increase specificity for glycogen is to digest the tissue with diastase (a glycogen-degrading enzyme) before the PAS reaction. If the magenta staining disappears after diastase treatment, the substance was glycogen; if it remains, the signal comes from non-glycogen carbohydrates. This combination (PAS with or without diastase) is therefore more specific for glycogen demonstration than Best carmine, which stains a broad range of carbohydrates without the enzymatic differentiation. H&E and silver stains are not as specific for glycogen, since they are not tailored to distinguish glycogen from other polysaccharides.