Which stain is used to detect amyloid deposits in tissue?

• A. Congo red
• B. Alcian Blue
• C. Giemsa
• D. Brown & Brenn Gram stain

Answer: (A)

Amyloid deposits are detected with a dye that binds to the beta-pleated sheet structure of amyloid proteins. Congo red fits this role: when tissue is stained with Congo red and viewed under polarized light, the amyloid exhibits an apple-green birefringence, which is diagnostic for presence of amyloid.

The other stains don’t target amyloid. Alcian Blue highlights acidic mucopolysaccharides and glycosaminoglycans, not amyloid. Giemsa is used for general cellular staining on blood smears and smears, not for identifying amyloid. Brown & Brenn Gram stain is a Gram stain used to differentiate bacteria, not to reveal amyloid deposits.