Which digestion reagent is commonly used but tends to loosen tissue sections and may not completely digest glycogen?

• A. Malt diastase
• B. Alpha amylase
• C. Protease
• D. Pepsin

Answer: (A)

Removing glycogen before PAS staining is done with a diastase digestion. Malt diastase is the reagent most commonly used for this purpose because it contains α-amylase that cleaves glycogen’s glucose units. This helps distinguish glycogen from other polysaccharides, since glycogen will be digested and lose PAS positivity.

But this digestion can loosen tissue sections because it breaks down carbohydrate components that help hold the tissue matrix together, especially if incubation is too long or the sections are thin or poorly fixed. In addition, glycogen digestion may be incomplete under routine conditions due to factors like fixation level, pH, temperature, duration, or section thickness, so some glycogen can remain and PAS positivity may persist in those areas. Proteases or pepsin would mainly digest proteins and would disrupt tissue structure rather than selectively removing glycogen, and while α-amylase is the enzymatic activity involved, the histology reagent used is typically described as malt diastase.