NI-301

Congo red amyloid staining is a histochemical method used to detect extracellular amyloid deposits in tissue sections based on the affinity of Congo red dye for β-pleated sheet-rich protein aggregates. When bound to amyloid, Congo red produces characteristic apple-green birefringence under polarized light microscopy, which is widely regarded as a diagnostic feature of amyloid deposition in histopathology. The diagnostic principle relies on the combination of dye binding (congophilia) and optical anisotropy under polarized illumination, which distinguishes amyloid from most non-amyloid eosinophilic extracellular deposits in routine histological evaluation. Amyloid identification by Congo red staining remains a cornerstone in diagnostic pathology despite the availability of adjunct methods such as immunohistochemistry and mass spectrometry, particularly because of its ability to localize deposits directly within tissue architecture. The specificity of Congo red-positive deposits is incre