What stains are used to demonstrate amyloid?

• A. Congo Red and Thioflavin T
• B. Congo Red and PAS
• C. Thioflavin T and Alcian Blue
• D. PAS and Hematoxylin

Answer: (A)

Amyloid is best demonstrated by stains that specifically bind to its beta-pleated sheet structure. Congo red binds amyloid and, seen under polarized light, yields apple-green birefringence—the classic hallmark of amyloid in tissue. Thioflavin T binds amyloid fibrils and fluoresces under UV or blue light, providing a sensitive confirmation. Using both stains together gives complementary evidence: Congo red provides the polarized-light signal, while Thioflavin T offers fluorescence confirmation. Other stain combinations don’t target amyloid specifically—PAS highlights carbohydrates, Alcian Blue stains acidic mucopolysaccharides, and Hematoxylin is a nuclear stain—so they aren’t used for demonstrating amyloid.