Which stain is used for demonstration of glycogen in tissue sections?

• A. PAS reaction
• B. Hematoxylin
• C. Alcian Blue
• D. Prussian Blue

Answer: (A)

Glycogen is best demonstrated with a colorimetric test that reacts with aldehyde groups created after oxidation of carbohydrate diols. The Periodic acid–Schiff (PAS) reaction does exactly this: periodic acid oxidizes vicinal diols in glycogen to aldehydes, and the Schiff reagent binds those aldehydes to yield a magenta (pink) staining where glycogen is present. This makes glycogen-containing areas stand out in tissue sections. For specificity, diastase digestion before PAS (diastase-PAS) can digest glycogen; if the magenta stain disappears, that confirms glycogen is the substance stained, while other PAS-positive substances like mucosubstances remain. Hematoxylin stains nuclei, Alcian Blue targets acidic mucopolysaccharides, and Prussian Blue marks iron; none are specific for glycogen, so PAS is the correct choice.