Diastase digestion increases the specificity of PAS staining for which substance?

• A. Glycogen
• B. Protein
• C. Lipids
• D. Nucleic acids

Answer: (A)

PAS reveals many carbohydrate-rich substances, including glycogen, mucopolysaccharides, and glycoproteins. When diastase (amylase) is used before PAS, it breaks down glycogen, so any PAS positivity caused by glycogen is lost. This makes the staining more specific for glycogen because a diastase-sensitive signal points to glycogen as the source of the PAS reaction. If the signal remains after diastase treatment, it suggests other diastase-resistant substances like mucopolysaccharides or glycoproteins are responsible. So diastase digestion increases specificity for glycogen in the context of distinguishing glycogen-derived PAS positivity from other PAS-positive substances. The other options—protein, lipids, and nucleic acids—are not selectively removed by diastase, so they don’t define the diastase-sensitive (glycogen) component of PAS staining.