Which stain is used to differentiate amyloid by Congo red staining?

• A. Congo Red
• B. Silver Stain
• C. Prussian Blue
• D. Masson\'s Trichrome

Answer: (A)

Amyloid identification relies on Congo red staining because amyloid fibrils bind this dye. When the tissue is stained with Congo red and viewed with polarized light, the deposits show an apple-green birefringence, which distinguishes amyloid from other tissue elements. The other stains serve different purposes—silver stain for reticulin networks or some organisms, Prussian blue for iron, and Masson's Trichrome for differentiating collagen and muscle—so they don’t provide the same diagnostic contrast for amyloid.