For PAS staining of glycogen in tissue, which fixatives are acceptable?

• A. 10% NBF, formalin alcohol or absolute alcohol
• B. Acetone
• C. Bouin's solution
• D. Guraldehyde solution

Answer: (A)

Glycogen preservation during fixation is crucial for a reliable PAS reaction, because the stain depends on accessible carbohydrate residues that can be oxidized to aldehydes and then detected by Schiff reagent. Fixatives that preserve glycogen without extracting it or masking its carbohydrate groups allow the periodic acid to generate the aldehyde sites needed for the Schiff reaction. Ten percent neutral buffered formalin provides good tissue structure while keeping glycogen in place, and combining formalin with alcohol or using absolute alcohol helps maintain glycogen availability during processing. These fixatives avoid the excessive extraction or over-crosslinking that can hinder the PAS reaction.

In contrast, acetone can be too harsh and may extract glycogen; Bouin's solution, which contains picric acid, can cause masking or extraction of carbohydrate residues or interfere with staining; and glutaraldehyde (Guraldehyde) cross-links tissues very strongly and can impair the oxidation step or Schiff reaction, leading to weak or inconsistent PAS staining of glycogen.