Which stain is commonly used to identify amyloid deposits in tissue sections?

• A. Congo Red
• B. Crystal Violet
• C. Thioflavin T
• D. Alcian Blue

Answer: (A)

Focusing on detecting amyloid deposits hinges on a stain that binds to the abnormal protein structure amyloid adopts. Congo red has a high affinity for the beta-pleated sheet conformation of amyloid. When tissue sections stained with Congo red are examined with polarized light, the deposits exhibit an apple-green birefringence, a distinctive diagnostic feature that confirms amyloid presence. This makes Congo red the stain of choice for routine identification of amyloid in histology. Other stains mentioned serve different purposes in tissue staining—crystal violet is a general dye used in other contexts, Alcian Blue stains acidic mucins, and Thioflavin T can label amyloid but is a fluorescence-based method and not as widely used for routine paraffin sections as Congo red.