Which fixatives are commonly used for preserving tissue prior to PAS staining?

• A. 10% Neutral Buffered Formalin or Bouins solution
• B. 70% Ethanol
• C. Acetic acid
• D. Glutaraldehyde

Answer: (A)

When performing PAS staining, you want a fixative that preserves tissue structure while keeping carbohydrates and mucopolysaccharides available for the Schiff reaction. Formalin, specifically 10% neutral buffered formalin, does this well by forming protein cross-links that maintain morphology without stripping away carbohydrate-containing components. Bouin’s solution, a picric acid–based fixative, also preserves glycogen and basement membranes effectively, and when thoroughly washed, works with PAS to reveal these substances clearly.

In contrast, ethanol tends to dehydrate and can extract soluble carbohydrates, which weakens PAS staining. Acetic acid alone causes tissue swelling and poor morphology, which isn’t desirable for accurate PAS interpretation. Glutaraldehyde fixes very aggressively and can mask carbohydrate residues, making the PAS reaction less reliable. So, the common choices for preserving tissue prior to PAS are formalin or Bouin’s solution.