The Schiff reaction may show false positives following chromate-containing fixatives.

• A. True
• B. False
• C. Not always
• D. Only with certain fixatives

Answer: (B)

Schiff’s reaction (PAS) detects carbohydrates by first oxidizing them with periodic acid to create aldehyde groups, which then react with Schiff’s reagent to give a magenta color. Chromate-containing fixatives cross-link tissues with chromium and do not generate aldehyde groups that would mimic carbohydrates; in fact, they tend to mask carbohydrate residues, often reducing PAS staining rather than causing a false-positive signal. So, you would not expect Schiff’s reaction to produce false positives simply because the tissue was fixed with chromate-containing fixatives. If staining is observed, it’s more likely due to other factors or non-specific background, not a true PAS positive from chromate fixation.