Tissue fixed in glutaraldehyde is not satisfactory for which histochemical reaction?

• A. The PAS reaction
• B. Hematoxylin staining
• C. Weigert’s iron hematoxylin
• D. Mucin staining

Answer: (A)

The main concept is how fixatives affect carbohydrate-detecting stains. Periodic acid–Schiff works by oxidizing carbohydrates to form reactive aldehyde groups, which then react with Schiff’s reagent to give a magenta color. Glutaraldehyde fixes tissues by creating extensive protein cross-links, which masks or blocks those carbohydrate residues and the aldehyde groups produced during the oxidation step. Because the aldehydes are blocked, the Schiff reaction can’t generate its color, making PAS staining unreliable on glutaraldehyde-fixed tissue. Other stains listed rely on other mechanisms or are less affected by this cross-linking, so they remain satisfactory.