Which statement about diastase digestion in PAS staining is correct?

• A. It removes glycogen, allowing differentiation of carbohydrate components.
• B. It stains glycogen more intensely.
• C. It preserves all carbohydrates.
• D. It digests proteins.

Answer: (C)

Diastase digestion in PAS staining tests how the tissue handles a diastase enzyme before the PAS reaction. Alpha-amylase digests glycogen, so when you treat tissue with diastase before applying PAS, glycogen is removed. This means any remaining magenta signal after the diastase step comes from diastase-resistant carbohydrates, such as certain mucopolysaccharides and glycoproteins, not glycogen. Therefore, the correct statement is that diastase digestion removes glycogen, allowing differentiation of carbohydrate components. It doesn’t make glycogen stain more, it makes it disappear; it also doesn’t preserve all carbohydrates—only glycogen is digested while other diastase-resistant carbohydrates may still stain. It also does not digest proteins, since diastase targets carbohydrates, not proteins.