In PAS with diastase digestion, what are the expected results for glycogen, neutral mucin, and acid mucin?

• A. Glycogen Negative; Neutral Mucin Positive; Acid Mucin Negative
• B. Glycogen Positive; Neutral Mucin Positive; Acid Mucin Negative
• C. Glycogen Negative; Neutral Mucin Negative; Acid Mucin Positive
• D. Glycogen Positive; Neutral Mucin Negative; Acid Mucin Positive

Answer: (A)

Periodic acid–Schiff (PAS) stains carbohydrates, including glycogen and mucins. When diastase digestion is added (PAS-D), the enzyme digests glycogen, so glycogen loses its PAS positivity. Mucins, however, have different carbohydrate components: neutral mucin contains neutral sugars that still stain with PAS after diastase, while acid mucins (sulfomucins and sialomucins) do not stain with PAS and are usually identified with Alcian blue instead. Therefore, after PAS-D, glycogen becomes negative, neutral mucin remains positive, and acid mucin remains negative.