Which staining pair is commonly used to identify amyloid deposits?

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

Answer: (A)

Amyloid has a distinctive beta-pleated sheet structure that stains specifically with dyes designed to bind that arrangement. Congo red binds to amyloid fibrils and, when examined under polarized light, shows an apple-green birefringence that is highly characteristic of amyloid deposits. Thioflavin T also binds to the beta-pleated sheet configuration and fluoresces under appropriate light, providing a sensitive confirmatory signal. Using these two together strengthens identification because one test highlights birefringence and the other highlights fluorescence, making the detection more reliable. Other pairs mix stains that do not specifically target amyloid—PAS stains carbohydrates, Alcian Blue targets acidic mucopolysaccharides, and Hematoxylin is a general nuclear stain—so they aren’t used together to identify amyloid.