Amyloid shows a yellow birefringence following staining with Congo red.

• A. True
• B. False
• C. It shows red birefringence
• D. It shows blue birefringence

Answer: (B)

Amyloid detection with Congo red relies on the characteristic birefringence observed under polarized light, which is apple-green, not yellow. Congo red binds to the beta-pleated sheet structure of amyloid, and when viewed with cross-polarized light, this arrangement produces the distinctive apple-green birefringence. Seeing yellow, or red or blue birefringence, is not the typical finding, so the statement is false. This apple-green birefringence is a key confirmatory feature of amyloid deposits.