Which histochemical stain is associated with removing glycogen using an amylase before staining?

• A. PAS
• B. D-PAS
• C. H&E
• D. Alcian Blue

Answer: (A)

Glycogen is a carbohydrate that PAS staining highlights because PAS reacts with polysaccharides to give a magenta color. Before this staining, treating the tissue with amylase (diastase) digests glycogen. If the PAS-positive substance is glycogen, this pre-digestion will remove that staining, and the magenta color will disappear after the amylase treatment. This combination—stain with PAS after diastase digestion—is a standard way to confirm glycogen as the source of PAS positivity.

So, the stain used in this context is PAS. The diastase step is a pretreatment to differentiate glycogen from other PAS-positive substances (like certain mucopolysaccharides or glycoproteins). H&E and Alcian Blue do not selectively test for glycogen in this way.