Amyloid can be demonstrated with which stain?

• A. Congo red
• B. Hematoxylin
• C. Mayer mucicarmine
• D. Toluidine blue

Answer: (A)

Amyloid deposits have a distinct structure that takes up certain dyes and shows a characteristic optical property under polarized light. The dye that binds tightly to the beta-pleated sheet arrangement of amyloid and reveals this property is Congo red. When tissue stained with Congo red is examined under polarized light, amyloid appears with apple-green birefringence, which is highly diagnostic for its presence.

Hematoxylin, a common nuclear stain, highlights cell nuclei and general tissue but does not specifically identify amyloid. Mayer mucicarmine stains mucin, not amyloid. Toluidine blue is used for metachromasia and general tissue features but not for confirming amyloid deposits. Therefore, Congo red is the stain that best demonstrates amyloid.